Operation 36

Operation 36 consists of six surface-visible edifices (Strs. 2, 47-51) set on to and slightly back from (south and east of) the edges of two adjoining depressions near the northern margins of La Sierra's North Cluster. Structures 47, 48, 49, and 51 occupy the southeast, northwest, northeast, and southwest corners of a patio while Strs. 2 and 50 lie immediately northeast of this aggregation. The depressions are oval-shaped, 1-1.2m deep, and run in a rough northwest-southeast line immediately north and west of the aforementioned buildings. The behavioral significance of these basins was not obvious from their surface forms and dimensions, and excavations were conducted here in 1990 to date their creation and infer their function(s). Operations 56, 31, 12, 16, and 54 bound Op. 36 on the north, east, southeast, southwest, and west, respectively. La Sierra's site core is approximately 165m south of Op. 36. The terrain encompassed by Op. 36 is fairly level, the land rising slightly away from the depression, north-to-south and west-to-east. A total of ca. 235m2 were cleared in the course of uncovering significant proportions of Strs. 2, 49, 50, and 51 during the 1990 and 1995 field seasons. In addition to the architecturally-focused investigations, 18 test pits, each measuring 0.5m on a side and spaced 5m apart, were excavated in a line bisecting the long axes of the two adjoining depressions (the 4.5m2 cleared in the course of digging these probes is included in the figure quoted above). The 1990 research was directed by E. Bell, the 1995 efforts being the responsibility of N. Gevock.

Structure 2 (Figures **-**) [2 plans, 2 sections; D95-1, 63 or 64]

Structure 2, the largest edifice included within Op. 36, appeared on the surface to consist of two distinct platforms joined by a low saddle. Excavations revealed that Str. 2 was a single,coherent building by the final construction stage, though it may well have begun as a pair of closely spaced but separate edifices. Situated 21m northeast of the Op. 36 patio, Str. 2 lies 12m in the same direction from Str. 50 and 10m north of Str. 1 in Op. 12. Its proximity to Str.1 suggests that Str. 2 was part of the Op. 12 aggregate; alternatively, the edifice might have been integrated within a group that was largely obliterated byy the construction of the adjoining access road, Strs. 110-112 in Op. 31 lying 10-22m to the northeast being remnants of that putative cluster. The close-spacing of constructions in the North Cluster renders the assignment of buildings to particular groups problemmatic and all divisions of the nearly continuous flow of architecture into operations arbitrary and this is certainly the case for Str. 2. The land on which Str. 2 was raised ascends gradually from north to south (rising 0.18m over 13m) and west to east (mounting ca. 0.3m over 12.15m). Approximately 94m2 were cleared during the investigation of Str. 2 from January 30-March 24, 1995 (Subops. 36H and I). Digging was carried down to maximum depths of 1.44m below modern ground surface outside construction and 0.9m beneath ground level into architectural fill. Two construction phases, together with evidence for a significant change in how the building was used late in its occupation sequence, were revealed in this work directed by N. Gevock.

Unit 1 is covered by Str. 2-1st's fill (U.30), runs for 1.4m, and is aligned roughly 91 degrees. Unit 2 is in the same stratigraphic position as, and 0.85m northeast of, U.1, measures 1.5m long, and is oriented 86 degrees. Unit 4, also buried by U.30, is 1.3m south of U.1, was exposed over a distance of 0.8m, and is aligned 6 degrees. Unit 3 was revealed in the floor of Room 1 on Str. 2-1st's southern summit, ca. 5.5m east of U.2. This construction measures 3.1m long and is oriented 82 degrees. The architectural significance of the above entities is far from certain. Given the location of U.1, 2, and 4 on what was probably ancient ground surface later covered by Str. 2-1st, these stone lines may well be the remains of foundations that defined the perimeters of surface-level buildings. It is unlikely that U.1, 2, and 4 were components of a single edifice; they probably represent fragments of three diminuitive constructions. How U.3 related to U.1, 2, and 4, if at all, and what purposes it served are not inferrable at present. All TS.2 architecture is built of unmodified river cobbles set in a brown mud mortar.

Structure 2-1st consists of two distinct segments that are linked on the north but separated by as much as 0.7m on the south. These elements may have begun as separate buildings that eventually coalesced into a single edifice, though this reconstruction is not established. The northern segment is nearly rectangular measuring 8.4m north-south by 4.7m east-west. and bounded by cobble retaining walls that rise a reconstructed 1m in a single steep ascent (U.5, 7, 8, and 10). Remnants of what may have been a 0.5m wide by 0.4m high stone-faced terrace (U.7) fronts the building on the north. Unit 7 intersects U.6, 0.85m short of the latter's northwest terminus, creating an inset corner that encompasses 0.6x0.85m. On the east, U.7 joins U.8, the apparent eastern platform facing that is overlapped by and incorporated within architecture associated with Str. 2-1st's eastern platform (U.13). This relationship imples that the latter was expanded westward after U.7 and 8 were already in place. A set of two barely discernible steps project 1.6m south of the western platform's southwest corner (U.11 and 12). The staircase is an inferred 1.8m wide, the risers ascending in intervals of 0.14m and 0.38m (basal (U.12) and second ascending steps (U.11), respectively) towards U.10, the southern basal wall. The U.12 tread is 0.5m wide, that backing U.11 measuring 1.1m across. There is a slight hint that a 0.25m wide stone balustrade (U.32) flanked the steps on the east (the west side was not investigated). All fill, including that retained by the principal basal walls (U.30) as well as that backing U.7 (U.31) and underlying the southern steps (U.33), consists of densely packed river cobbles suspended in a brown earth matrix. The summit was revealed only in the 1m wide north-south trench that cuts across the entire building. Based on this limited exposure, it appears that Str.2-1st's western step, terrace, and summit surfaces were earthen.

The eastern platform is, despite its irregular eastern and western outlines, nearly square, measuring 7.3m north-south by 7.5m east-west. The basal walls (U.13, 15, 22, 23, and 24) rise approximately 1m to the summit which consists of a single room that encompasses 2.9x4.7m (Room 1; measured across the center). On the north, a ca. 0.2m high terrace (U.14) intervenes between the basal wall (U.13) and the summit. The eastern facing (U.15 and 22) is by far the most irregular basal wall on the building. Unit 15 extends 1.7m south from its junction with U.13 at the platform's northeast corner until it encounters U.20, the 1m wide stone balustrade that delimits the northern boundary of the eastern staircase. Unit 20 is roughly 3.35m long east-west and its northern facing continues westward to where it intersects U.8, the western platform's eastern basal wall. Given that U.13 overlaps U.8 by 0.5m and U.20 apparently abuts that facing, we would guess that U.20 is an earlier version of the eastern platform's northern basal facing, eventually superseded by the addition of U.13 and 14.

The eastern staircase is 1.85m wide and consists of three stone-faced risers (U.16, 17, and 18, in ascending order), the basal step even with U.20 and the platform's eastern facing. Each stair is 0.2-0.4m high, the treads vaying from 2m wide (the lowest) to 0.6m across. Unit 21, a 0.6m wide by 3.1m long balustrade, bounds the stairs on the south and projects 0.6m east of U.16. Unit 22 then continues the eastern facing 2.4m south from U.21, joining with U.23 to create the eastern platform's southeast corner. An enclosure set ca. 0.7m above ancient ground surface and paved with cobble (U.25) bounds the U.21 balustrade on the south (Room 2). This space, which covers 1.7x2.7m, is closed by an approximately 0.7m high by 0.75m wide cobble step-up to the summit on the west that may well have doubled as a foundation for the superstructure's perishable upper walls. Room 2 appears to have been open on the east and south. No furniture or other architectural elements were detected within Room 2's confines.

The eastern stairs issue onto a 1.95x2.15m cobble surface (U.19) that may have been a landing formalizing passage through the 1.3m wide doorway (between U.20 and 28) into Room 1. The remainder of the enclosure is surfaced with earth and lacks recognizable built-in furniture assignable to TS.3. Unit 29, a 1.4m long cobble line that appears to continue the southern facing of the U.21 balustrade into Room 1, is 0.8m south of U.19 and may have been part of an effort to partition that summit compartment. The dimensions and significance of this entity remain as obscure now as they were in the field, however, and we will advance no further opinions concerning its architectural role(s).

A very limited portion (0.22m thick) of the eastern platform's architectural fill (U.34) was revealed in a probe dug beneath the summit. Unit 34 is a tan (brownish-yellow, 10YR-6/6) clay containing artifacts but relatively few stones.

By the conclusion of TS.3, Str. 2-1st was a ca. 1m high platform composed of two disparate elements; a western rectangular construction covering 4.7x8.4m and oriented roughly 1 degrees an an eastern component that encompasses 7.3x7.5m and is aligned very approximately 358 degrees. Steps bounded by stone balustrades facilitate passage to the summits of both entities, a staircase projecting 1.6m south of the western platform's southwest corner while a set of three steps begin even with the eastern platform's east face and lead to a cobble-paved landing at the 1.3m wide entrance to the summit enclosure. Almost all of the eastern platform was cleared, revealing a large summit compartment (Room 1, 13.6m2) and a smaller enclosure lying east of, and slightly below, the summit (Room 2, 4.6m2). The latter has a cobble floor while the former, aside from the paved landing (4.2m2), is surfaced with earth. No benches, shelves, or other built-in furniture was identified in either room, though it is entirely possible that any such constructions might have been dismantled during TS.4 when the summit was heavily modified. An insufficient amount of the western platform's summit was cleared to determine the nature and organization of its superstructure. All walls and floors are fashioned primarily of unmodified river cobbles set in a brown mud mortar. A few schist slabs were noted within the eastern stairs, especially in U.18, the uppermost step. Though far from clear, it seems plausible that the eastern platform was expanded 1.6m northward by the addition of U.13 and 14 sometime after the western platform had reached its ultimate northern and eastern extent (as represented by U.7 and 8).

Unit 27 was only cleared over a northwest-southeast distance of 1.3m ca. 0.7m west of U.26. Time did not permit excavation within the area defined by this arc and so we could not ascertain what sorts of material were associated with the construction. Extrapolating U.27's lines out tentatively suggests that this construction was larger than its eastern counterpart, measuring very approximately 2m across and probably continuing onto uninvestigated portions of the western platform's summit. Unit 27 is seemingly built over U.8's eastern face, the latter not being found in this area (though it is clear enough north and south of the arc). Construction of U.27 probably contributed to the disruption of U.8, indicating that the former's erection postdates the latter.

Two gaps were apparently cut at floor level into the northern (U.8) and southern (U.28) summit margins at this time. The former is 0.4m wide and located 1m north of Room 1's southwest corner. Its eastern counterpart is 0.8m north of the enclosure's southeast corner and 0.7m across. These gaps face eachother across a distance of 2.7m, a line drawn between their centerpoints running 0.4m south of U.26 and 1.4m south of U.27. It is not certain that either gap penetrates the full width of the walls in question, disruptions to both U.8 and 28 being so severe as to render any decision on this issue moot.

All construction dating to TS.4 is fashioned of unmodified river cobbles set in a brown earth matrix. There is no clear tendency to orient the naturally flatter aspects of these rocks outward and the architecture in each case seems quite casual. Unit 26 and, possibly, U.27 are the remnants of pits whose use involved intense burning. The gaps cut into U.8 and 28, if they pierce completely through both walls, may have been fashioned to allow the passage of air needed to fuel the putative fires. Such activities do not seem compatible with the size and relative elaboration of Str. 2-1st with its elaborate eastern entryway. Instead, we would argue that the constructions described above were introduced after Str. 2-1st had been abandoned for awhile (hence its poor state on preservation when excavated). For whatever reason, the ruin was judged appropriate for the conduct of a different set of activities than its original builders had envisioned, behaviors that could yield heat great enough tio melt and vitrify bajareque fragments.

Unit 2 was exposed within what would later become the confines of Str. 49-1st's Room 4. This cobble line was revealed for a distance of 2.1m. Unit 2 is roughly 0.25m wide and is aligned at a markedly different azimuth (ca. 294 degrees) from the Str. 49-1st components that surround it. Though it is difficult to reconstruct Room 4's floor level, U.2 certainly does not protrude much above, and was probably flush with, the living surface contained within the enclosure. This stratigraphic relationship, coupled with U.2's divergent orientation, leads us to argue that the element in question is a component of an earlier version of the principal building (tentatively designated Str. 49-2nd). Most likely, U.2 is part of a footing incorporated within a surface-level building that was largely razed during TS.3 construction. Units 1 and 2 could conceivably be parts of the same edifice, though this notion was not evaluated in the field.

Both U.1 and 2 are fashioned of unmodified river cobbles set in a brown mud mortar. Insufficient expanses of these constructions were unearthed to reveal more information on their architectural forms.

Units 22-24 combine to facilitate and channel passage onto the extensive southwestern terrace (covering ca. 11m2) running 2m back (northeast) to the next ascending riser (U.6, 0.22m high). This area is defined by U.3 and 6 ascents on the southwest and northeast as well as by the broad U.4 and 5 walls on the northwest and southeast. The former measures 0.85m across but is preserved to only 0.09m high. Unit 5 is roughly 0.9m wide and rises 0.35m. Built into the northern corner of the southwest terrace is an 0.18m high stone-faced bench (U.7) that is 0.9m wide by 2.1m long (measured across the center). Unit 7 faces southwestward over the U.3 terrace riser. The only other extant architectural elements found on the southwestern terrace are U.8 and 9, rectangular cobble blocks that define the northwestern and southeastern sides of an entry feature in line with the approximate center of the southwestern steps (U.22-24). Unit 8 is 0.5m wide and extends 1.3m southwest from U.6; it had been heavily damaged since last used and the 0.04m preserved height is almost certainly not its original dimension. Unit 9 is 0.4m wide, 0.34m high, and projects 1m southwest from U.6. Though most of the southwestern terrace is surfaced with earth, the 0.65x1.3m delimited by U.6, 8, and 9 is at least partially paved with four to five cut blocks that were in a fragmented state when found (U.10). It appears that the masonry had been broken in place. This damage may have been a consequence of repeated use, though it is hard to imagine that simply walking over the stones would produce this result. More likely, the breakage was deliberate.

Passing between U.8 and 9 and up the 0.22m high ascent of U.6 leads to a 1.2m wide by, very approximately, 1.7m long cobble pavement (U.11) that ends on Room 3's southwestern margin. Flanking U.11 on the northwest and southeast are Rooms 1 and 2. Both are earthen-floored compartments bounded on all sides save the southwest by low cobble footings (U.4, 12-14, preserved 0.08-0.23m high) and lack extant built-in furniture. The southwestern flank in each case seems to have been open, overlooking U.6. Room 1 encompasses 1.25x3m and may have been accessed both from U.11 on the southeast and through a 0.4m wide gap between the U.12 and 16 foundations in the enclosure's northern corner. The latter passage would have afforded direct access to Room 3. Room 2 covers 1x1.4m and there seems to have been a 0.4m wide door set into its eastern corner. The putative doorway in Room 2 only seems to lead to a 0.4x1.5m space sandwiched in between the southeastern room's footing (U.14) and Str. 49-1st's southeastern perimeter wall (U.5).

Room 3 is an extensive (ca. 1.3x5m) earthen-floored compartment that seems to have been the destination to which the various entry features were leading (U.22-24, 8-11). The western and northeastern perimeter foundations (U.5, 16, 21, and 25) of Room 3 define an irregular boundary, varying considerably in orientation. These discrepancies tentatively suggest that the compartment was created in the course of several construction episodes during which the space was gradually enclosed by footings measuring 0.22-0.8m across and standing 0.12-0.38m high. set in the approximate center of the room, facing the long northeast-southwest trending entryway is a 0.4m high stone-faced bench (U.15). Built against the northeastern foundation (U.21), U.15 is approximately 1m wide by 1.9m long (its northwestern and southeastern ends were not clear and so the length given above is no more than an approximation).

Room 4 backs Room 3 on the north, U.21 acting to separate the two compartments. The former enclosure is roughly L-shaped, the step running nearly east-west and the leg projecting northward from the figure's east end. Overall, Room 4 emcompasses 4.3m2. Those foundations bordering Room 4 on the west, north, and east (U.16-20) appear to have been added in segments and are oriented very differently from most of Str. 49-1st's architectural features southwest of U.21. This pattern suggests that Room 4 was created piecemeal relatively late in the construction sequence . Units 16-20 are 0.2-0.8m wide and stand 0.15-0.26m high. Room 4's earthen surface, which may have been tilted slightly downslope to the north, supported no extant built-in constructions. There is a 0.3m wide gap in Room 4's northern perimeter between U.17 and 18. This interruption seems too narrow to have been a doorway and may be related somehow (possibly as a vent) to activities conducted around F.1.

Located immediately north of Room 4, in the area defined by U.16, 17, and 18, is a bajareque concentration measuring 0.6x0.7m. The wattle-and-daub fragments are overlain by a level of fine-textured gray ash that continues southward and eastward for roughly 0.9m (all glossed as F.1). The significance of this concentration is unclear. It most likely represents the remains of a wattle-and-daub construction set within a space that was sheltered on the east and south (U.18 and 17) by foundations and the walls they supported but was largely open on the north and west. The ash included in F.1 implies that it is the remnant of an oven.

A second bajareque concentration (F.2), this one covering 0.87x1.4m, lies 0.5m south of the U.24 step and adjoins U.22. Feature 2 may continue further south than the 0.87m figure indicates, excavation stopping before the bajareque's southern limit was rached. The architectural significance of this concentration is unknown.

Units 26 and 27 are 0.57m and 0.22m high cobble terraces that run more-or-less parallel to each other 1.5m and 2.32m north of Str. 49-1st. A 0.5x0.75m indentation marks U.27's northern face; no comparable element was found in U.26. These constructions are set well up on the southern margin of the northern depression and were seemingly built to slow erosion below Str. 49-1st into the basin. A fine-textured, gray ash (S.1) extends from the base of U.26, over U.27 and continues at a downward slope, descending 0.83m across 3.21m south-to-north into the pit. Stratum 1 is exposed to maximum thickness of 0.23m (the base was not found) and appears to represent debris generated by activities that occurred further upslope, probably on and around Str. 49-1st. This patterning suggests that the behaviors in question involved a considerable amount of burning and, by the end of TS.3, at least part of the northern basin was being used as a trash receptacle. The putative F.1 "oven" is the most likely source of S.1.

Unit 28 is a cobble line that was uncovered for a distance of 1.2m, lying 0.25m east of U.20 and 1.5m north of U.25. Based on its depth, U.28 appears to be contemporary with neighboring components of Str. 49-1st construction, though it is not clearly linked to any of them. Possibly, U.28 is part of a foundation for yet another enclosure built adjacent to (east of) Room 4 and bounded by U.20, 25, and 28 on the west, south, and north. If so, the compartment would have measured 1.7m north-south (across the center) and been open on the east.

Overall, Str. 49-1st is a building that stands 0.72m above ancient ground surface on the southwest, but apparently rests directly on an ascending ground level on the north, covers 7x7.6m (measured across the center), and is oriented approximately 283 degrees, 30 minutes (southwestern portion) and 359 degrees (on the north). Entrance to Str. 49-1st was from the southwest where a series of access features channeled passage over steps (projecting minimally 1.85m southwest of the first ascending terrace), through a narrow corridor paved with fragmented masonry blocks (U.8-10), and onto a stone floor (U.11) that led directly to the largest enclosure, Room 3. The latter covers 6.5m2 and contains a 0.14m high stone-faced bench measuring 1m across by, approximately, 1.9m long. The bench faces directly into the entry corridor. Bordering U.11 on the northwest and southeast are two earthen-floored rooms that encompass 3.8m2 (Room 1 on the northwest) and 1.4m2 (Room 2). Both could be entered from U.11 and are equipped with 0.4m wide doorways that Connect Rooms 1 and 3 and Room 2 with a small (0.6m2) cubicle on the southeast. Room 4, an L-shaped compartment lying immediately north of Room 3, covers 4.3m2 and lacks built-in furniture. Another enclosure, measuring 1.7m across north-south, may have adjoined Room 4 on the east. Though it is difficult to determine, Rooms 1-4 and the putative eastern compartment appear to have been built directly on ground surface. The 11m2 encompassed by the first ascending southwestern terrace appears to have been raised above this level at least on the southwest. In addition to U.8-10, this terrace supported a 0.18m high stone-faced bench that measures 0.9x2.1m. The southwestern terrace is also characterized by inset corners on its northwestern and southeastern margins. A bajareque oven may have been in operation just north of Room 4, the latter's foundations helping to shield the construction on the east and south. Two stone-faced terraces 0.57m and 0.22m high are 1.5m and 2.32m north of Str. 49-1st. These entities are built into the upper margins of the northern depression and probably served to slow erosion down the relatively steep slope bounding Str. 49-1st on this side. An ash deposit overlying and extending 2.41m north of these terraces may well have derived from the putative oven noted earlier. Identification of this debris within tghe basin suggests that the northern declivity was being used as a trash container by the end of TS.3.

Except where noted otherwise (U.10), Str. 49-1st's facings, footings, and pavements were fashioned primarily of unmodified river cobbles the naturally flatter aspects of which were directed outwards. Cut blocks are the sole material used to make U.10 and a few pieces of masonry are incorporated in U.4, 13, and 24. Schist slabs appear in the U.11 and 29 floors and some are included in U.7 and 27. Horizontal coursing of the larger rocks is variably manifest in Str. 49-1st's walls, most being so badly preserved that identification of this feature was thwarted. Chinking stones appear to have been used to fill in the spaces among the more sizable cobbles in most cases. the southern faces of U.15 and 21 were built over at least part of their extents using vertically set cobbles backed by horizontally placed stones. This technique may have been restricted in U.21 to that portion backing the U.15 bench--once again, post-occupation disturbances made establishment of this point difficult. Rock sizes ranged from 0.04x0.07m to 0.16x0.67m, with most falling towards the middle of that continuum, e.g., 0.12x0.28m. A brown mud mortar was used as a binding agent in each unit.

Room 3, a tamped-earth-floor enclosure covering 1.04x1.5m, is built off the southwest corner of the Str. 50-1st platform. This compartment is bounded by foundations (U.9-12), measuring 0.2-0.6m across by 0.09-0.24m high, set directly on ancient ground surface and by the platform's southern basal wall (U.5). The northern footing (U.9) is the least substantial component of Room 3, being only one stone wide (0.2m). Unit 9 also does not run a straight course, extending 0.5m south from its junction with U.5 and then turning to run 0.86m east to intersect the eastern foundation (U.10). The result of this dog-leg is the creation of a 0.5x0.62m inset in the northern portion of Room 3. Unit 12, the western foundation, projects 1.65m south of Room 3. This extension, together with Room 3's southern footing (U.11), define a space measuring 1.65x1.8m open on the east and south. A large number of artifacts were recovered from the temped earth floor bounded by U.11 and 12, suggesting that this area served as a distinct activity area.

Room 4 was fashioned by the simple expedient of enclosing a portion of the space between Strs. 50-1st and 49-1st by low cobble foundations measuring 0.3-0.35m across. The southern limit of Room 4 is defined by U.13 which extends 1.2m northwest from U.12 and stops a scant 0.2m shy of Str. 49-1st's eastern perimeter wall (U.5). Unit 14 is an L-shaped footing that runs 0.8m east from Str. 49-1st's U.5 before turning south for 0.65m. The earthen-floored space enclosed by U.12-14 and Str. 49-1st's U.5 covers roughly 2.1m2 and could have been entered through a 0.7-0.8m wide doorway on the north between U.2 and 14. Unit 18, a 0.1m high by 0.5m wide cobble wall cuts east-west between U.12 and Str. 49-1st's U.5 0.3m north of U.13. The architectural significance of U.18 is not obvious. It is unlikely to have been the northern wall of a cubicle measuring only 0.3m across. More plausibly, U.18 may have been the northern face of a 0.1m high shelf encompassing 0.8x1.2m, U.13 marking the back of that construction.

Unit 15 is a low, 0.4m wide cobble wall, built in ancient ground level, that projects 1.3m north from U.3, 1.2m west of that facing's intersection with U.4. This element may be a footing that bounds an earthen-floored, surface-level room on the west. The southern side of the putative enclosure would is demarcated by U.3 while the north and east may have been left open. Alternatively, additional excavation in these directions might have encountered other components of the tentatively identified surface-level room.

Structure 50-1st's platform is 0.45m high, covers 3 x 4.5m, and is aligned roughly 103 degrees. The superstructure was divided into two compartments arranged in an east-west line, the roof supported, in part, by a sizable (ca. 0.35m diameter) center post packed round with, and shored up by, cobbles. The western enclosure measures 2m2 while its eastern neighbor encompasses 2.5m2 and has a 0.13m high shelf built into its northern wall. The shelf is 1m wide by 1.2m long. Surrounding the platform on, at least, the south, west, and north are the remnants of surface-level rooms. Room 3, lying immediately to the south, covers 1.9m2 and is bounded on the south by an activity area bordered by cobble foundations on the north and west but apparently open to the east and south. Both Room 3 and its southern neighbor have tamped earth floors on which sizable numbers of artifacts were found. Room 4 is bounded by Strs. 49-1st and 50-1st on the west and east, the southern and northern limits demarcated by low cobble foundations. This enclosure covers 2.1m2 and has a 0.1m high shelf that measures 0.8x1.2m built against the southern wall. North of Str. 50-1st's platform there may have been another room or activity area bounded on the west and south by a low cobble foundation and the platform's northern basal facing, respectively. Like the activity area south of Room 3, this northern space rests on ancient ground surface and may have been open on two sides (east and north in this case).

The Str. 50-1st complex almost certainly grew up over a protracted period. The rooms and activity areas built against the platform were erected after the latter was in place. Rooms 3 and 4, in particular, must have been built after the southern addition to the platform's basal wall was completed (U.5 sealing the earlier U.1 facing, see above) as both incorporate U.5 in their constructions. This observation also indicates that the platform itself underwent renovations over time. It is even possible that Str. 50-1st's core began its use-life as a surface-level building. The eastern 1.4m of U.3, the northern facing, is narrower than the rest of the wall and seems to have been built of generally smaller stones than is the case in the other platform facings. It may be that the above segment seals an earlier doorway, thus accounting for the discrepancies in construction. Transformations of surface-level edifices into platforms are attested to elsewhere in the Naco valley, though this modification is only suggested, not established, for Str. 50-1st.

All facings, foundations, and floors associated with Str. 50-1st are built primaily of unmodified river cobbles set in a brown mud mortar. The naturally flatter aspects of these rocks are directed outwards in the footings and basal walls and there is a tendency to arrange the larger rocks into horizontal courses. Chinking stones are used to fill in the interstices among the more sizable stones, though they are not equally common everywhere; these small pebbles are especially prevalent in U.4 where they also serve as a foundation for the larger rocks. Cut blocks are virtually non-existant within Str. 50-1st architecture, though one piece of masonry was found protruding 0.2m east from U.10. Rock sizes range from 0.04x0.05m to 0 0.1x0.46m, with most occupying the middle of that spread, clustering around 0.1x0.2m.

Capping S.1 on the south is S.5, a very fine-textured gray ash containing sizable quantities of artifacts. Stratum 5 is 0.02-0.08m thick, conforms to the underlying slope of S.1, rising 0.2m across 1.04m south-to-north, and ends on the north against S.6. The latter is a light tan sandy soil that contains relatively few artifacts. Stratum 6 blankets S.5 by 0.05-0.17m over all of its revealed 1.04m north-south extent; north of that point, S.6 drops down to replace S.5 on the upward ascent towards Str. 51-1st construction site. Over this 2.1m, therefore, S.6 first ascends dramatically, following the contours of S.1 and 5 which it covers for 1.04m, and then begins a more gradual upward slope ( rising 0.22m over the first 1.04m douth-to-north and then 0.11m across the remaining 1.06m in the same direction). Stratum 6 was also found underlying Str. 51-1st's basal northern construction (U.9) by at least 0.15m (its base was not encountered). On this flank, however, the complex earth stratigraphy seen further south was not identified, in part because digging was not pursued to a sufficient depth to locate S.1-5. A lens of fine-textured, gray ash was identified ca. 0.3m below U.7 on the north (not portrayed on the section). Only 0.04m of this deposit was exposed. The above lens may be a northward continuation of S.7-- the two are similar in composition and at about the same level, but they were not linked through excavation. The stratigraphic situation is not clear on the east. Here, excavations encountered very large quantities of artifacts, especially sizable pottery sherds, extending for at least 6m beyond construction. This deposit may represent a continuation of S.7, though we remain unclear concerning the matrix in which the artifacts were found.

Restricted excavation is not the only factor in the observed divergence in stratigraphic sequences. South of Str. 51-1st, S.6 is covered by S.7, a very fine-textured, soft-compacted, light gray soil in which large quantities of artifacts, especially sizable pottery sherds, are found. Stratum 7's deposition was interrupted over part of its extent by the introduction of a substantial lens of S.6. This layer is ca. 0.22m thick and measures 2.58m north-south. Contained within the S.6 lens is a deposit of very fine-textured light gray ash (S.8) that protrudes 0.05m above the base of excavation and was exposed for a north-south extent of 0.2m. Stratum 8 is located at the northern revealed margin of the S.6 lens. Stratum 7 is deposited around and over the S.6 intrusion. We estimate that 0.54m of S.7, in which the S.6 deposit is found, was laid down in TS.1 prior to Str. 51-1st's erection. Excavations north of Str. 51-1st yielded no signs of S.7 though digging on the west uncovered S.7 extending for 2.37m away from final-phase architecture (U.2). In the latter area, S.7 was only exposed to a maximum depth of 0.1m and rose 0.14m across 1.2m east-to-west.

The stratigraphy revealed south and, to a much more limited extent, west of Str. 51-1st suggests a prolonged human occupation here prior to that building's construction. Human presence in the area may have intensified, or the investigated zone was transformed into a major trash dump, late in TS.1 (represented by the extensive S.7 deposit). The large quantities of ash and artifacts recovered south of Str. 51-1st support this interpretation. It may be that S.7 was the product, not of gradual debris accumulation, but was purposefully introduced as fill to raise the living surface south and west of Str. 51-1st (that base of that platform's southern facing [U.1] is 0.49m higher than that of its basal northern architecture [U.9]). Similar uses of ash are inferred in Op.31 to the northeast. Whatever the cause of S.7's original deposition, it continued to be laid down south of Str. 51-1st throughout the suceeding two time spans.

Feature 1 is a rough stack of cobbles noted in the west excavation wall 0.34m south of U.1 (measured from U.1's southern face to the presumed northern limit of F.1). No obvious wall was encountered during excavations in this area. The regular placement of the F.1 stones and their stratigraphic position (extending down and up to U.1's base and top) tentatively suggest that these rocks may be the remnants of a casual construction added on to Str. 51-1st near the end of TS.2. Feature 1 may have been part of a southern basal facing that replaced U.1, expanding Str. 51-1st 0.66m to the south. The 0.34m between U.1 and F.1 is filled with S.7. Accumulation of S.7 apparently persisted throughout TS.2. This interpretation is indicated by the disposition of stone debris tumbled from final-phase architecture in TS.3 (F.2). The F.2 rocks sit in S.7 roughly 0.1m above the level to which S.7 had collected by the conclusion of TS.1. Assuming that this construction debris came to rest on or near the ground surface exposed during Str. 51-1st's use-life, then the location of F.2 implies that approximately 0.1m of S.1 was laid down between TS.1 and the beginning of TS.3. There is no sign of S.7 north of Str. 51-1st and this layer does not seemed to have been augmented west of the building during TS.2.

Structure 51-1st is a 0.53-1.08m high stone-faced, stone-and-earth filled, platform that measures 4.1x5.85m (not including the northern steps and F.1) and is aligned roughly 8 degrees. The building is ascended on the north by four steps that project ca. 3m from the platform into the patio and extend progressively eastward north-to-south towards the platform. The stone-faced risers are 0.06-0.44m high, though the second ascending stair may only have been visible where it was not covered by the basal step. The latter was apparently added fairly late in the construction sequence and obscured the second riser. Treads are 0.52-1.35m across and are surfaced with earth. A single, 0.13m high, terrace intervenes between the southern basal facing and the summit, the patterning of terraces on the east and west is unknown. Very little superstructure architecture was cleared, the summit apparently having supported a building composed of earthen-floored rooms bounded by cobble foundations. The platform may have been expanded 0.66m southward by the addition of a basal facing (F.1) that encased its predecessor (U.1) late in TS.2. Artifact-rich gray ash continued to collect against the building's southern facing during this interval, though this material may not derive from activities conducted on Str. 51-1st.

Foundations, steps, and basal walls are built of unmodified river cobble the naturally flatter aspects of which are directed outwards. Unit 3, however, incorporates a few cut blocks among the cobbles. Post-abandonment dislocation of building stones has been so extensive that it is difficult to infer architectural style. There seems to have been a tendency to arrange the larger cobbles within hoeizontal courses in some of the taller walls (i.e., the platform facings), some chinking stones being packed around the more sizable rocks. We are not certain how widespread this practice of coursing was. A brown mud mortar was used as a binding agent in all foorings, facings, and stair risers.

Time Spans (Southeastern Depression)

Stratum 1, therefore, intially descends 0.5m over 11m southeast-northwest, in keeping with the general slope of the Southeast Depression's southeastern margin, and then drops at least 1.4m across at least 11m in the same direction. Subsequently, S.1 rises, very approximately, 0.8m over 6.3m and 1m across across an additional 11m southeast-northwest but does not reappear further northwest. The three northwesternmost test pits (Subops. 36O-Q) should have been deep enough to reach the top of this level if it continued at the same elevation to the northwest.

Stratum 1's undulating surface can not be reconstructed in any detail from the limited exposures sunk along the Southeast Depression's center-line. Replacement of this layer to considerable depths by S.2 and 3 in Subops. 36H and K indicates that something occured to interrupt S.1's distribution in this area. It is not until Subop. 36N, ca.38.75m to the northwest, that S.1 regains the same elevation it exhibited on the declivity's southeastern edge in Subop. 36D. There is no evidence for any natural process that might have caused this break in S.1's horizontal distribution and the most likely interpretation is that the clay was removed by human action over an area measuring, roughly, 39m northwest-southeast. This digging reached depths of ca. 2m below the basin's margins near its center, the deepest portion concentrated in a space encompassing roughly 17.3m across northwest-southeast. The purpose of these excavations was, most likely, to acquire the clay that borders and underlies the modern declivity.

Recovery of artifacts from throughout S.1 on the southeast (Subop. 36D, E, and G) points to a human presence in the vicinity while this clay was being deposited. Stratum 1's manifestations further to the northwest in Subops. 36L and N did not yield cultural material, though both represent very limited exposures (0.5x0.5x0.1m). It may be, however, that S.1 was laid down over a protracted period and its deeper segments were introduced prior to substantial settlement in this portion of La Sierra. The forgoing interpretation presumes that S.1's upper portions on the northwest were dug away in antiquity, replaced by S.2 and 3 during a long episode of infilling; on the southeast, S.1 may have been left largely intact, still containing artifacts introduced during late accumulation of this clay. In fact, S.1's deposition may not be restricted to TS.1 on the southeast, but may have collected throughout the entire reconstructed sequence in this zone.

The combination of sand and river-rounded pebbles in S.2 implies that this level is of riverine origin, possibly deposited during floods from the Quebrada **, ca. **m to the west. The general absence of cultural material within S.2 further hints at a natural source for this sand and gravel.

Several interpretations could be offered for this distribution, though neither can be established based on the available data. In one scenario, S.3 fills in two depressions cut into S.2, these declivities measuring roughly 17.5m (minimally) and 19.5m across northwest-southeast, separated by ca. 6.5m of undisturned S.2. Alternatively, the lower portions of S.2 may have been introduced first into the Southeast Depression, subsequently covered completely by S.3. A later event removed approximately 6.5m of S.3 (measured northwest-southeast) that was later replaced by continued deposition of S.2. In either case, both S.2 and 3 seem to have been laid down within the Southeastern Depression during a period of infilling after the basin had been dug and abandoned.

Stratum 3 contains varying quantities of artifacts, particularly dense deposits of material, primarily large pottery sherds, being found within Subops. 36H, K, and Q. In the first two cases, cultural remains were concentrated between 0.6-1.4m below modern ground surface while in Subop. 36Q the objects were found primarily between 0.4-0.6m beneath ground level. The presence, and in some cases, the prevalence, of artifacts in S.3 suggests that trash jettioned from nearby buildings was washing down into the basin during TS.3. The sizable vessel fragments found within the three identified concentrations implies that some of the objects incorporated in S.3 were purposefully tossed into the depression, their large sizes indicative of relatively quick burial. The Southeast Depression, therefore, may well have been used as a receptacle for debris generated by activities conducted around its margin as well as a collecting place for objects that only gradually, and over long periods of time, worked their way down its slopes.

Time Spans (Northwestern Depression)

Time Span 1

The first activity recognized in the Northwest Depression is the laying down of S.1, a brown to very dark brown (10YR 2/2, 3/4, and 5/3) sand incorporating differing quantities of gravel. Inclusions become more frequent and larger from southeast to northwest in the test pit sequence. Stratum 1 was exposed to thicknesses of 0.1-0.3m in the bottoms of Subops. 36S-W in the declivity's center and on its northwestern and southeastern slopes. The top of this layer is found at 0.82-1.15m below current ground surface, the greatest depth reached in the approximate center of the basin (Subop. 36U). Like its counterpart in the Southeast Depression (S.2), S.1 usually contains no cultural material. A striking exception is attested to in Subop. 36V where large quantities of artifacts, especially ceramic sherds, were found throughout the 0.3m exposed portion of the layer and may well have continued deeper (excavations were terminated before the artifacts ran out). The reason for this divergence from the norm is not known. Given that the artifact concentration extends 0.3m into overlying S.3, it may be that the objects found within S.1 had percolated downwards from a later deposit. This interpretation does not account for the sizable quantities of cultural material found throughout the revealed portionof S.1.

Like the Southeast Depression's S.2, S.1 appears to derive from floods of a nearby watercourse. Given the northwest-southeast decline in included gravels, the source of the inundations may lie in the former direction, possibly the Quebrada ** currently situated **m to the northwest. Most likely, S.1 and 2 were laid down as parts of the same flooding episodes following the excavation of both declivities. If this is the case, then we did not pursue excavations deep enough in the Northwest Depression to encounter the clay that presumably lies beneath the sand. The earliest material encountered here, therefore, would be contemporary with the Southeast Depression's TS.2.

Stratum 2 seemingly represents a lengthy period during which the Northwestern Deperession was gradually filled in by the natural deposition of fine-textured soils. The artifacts dispersed throughout S.2 and 3 probably were washed down from the declivity's margins and are not the results of purposeful trash disposal. The especially dense concentration of cultural materials spanning the S.1/3 divide in Subop. 36V may be an exception while the rich artifact deposit at S.3's top in Subop. 36W most likely represents debris fallen from a nearby building raised on the basin's northwestern edge.

The appearance of clay blanketing sand (S.2- 4 over S.1) suggests that those natural forces that produced the extensive clay deposits underlying and surrounding La Sierra resumed operation after a period of flooding. There is no clear evidence that the clays laid down in TS.2 and 3 were mined by La Sierra's prehistoric inhabitants; S.2-4 may have filled in a large borrow pit created and abandoned at some earlier date.

All of the investigated edifices reached their final forms during Late Classic II, III. Based on the paucity of Late Classic III markers in relevant deposits at Strs. 49-1st, 50-1st, and 51-1st, the preceding edifices may have been erected relatively early within this span. Both the Southeast and Northwest Depressions continued to fill in with soil and debris now, though the sedimentation process certainly persisted well after occupation in Op. 36 ceased. Use of Op. 36 into Late Classic III is possible, though markers for this time period are not very common; if settlement extended into Late Classic III, it was not substantial nor was it clearly linked to any uncovered construction. There is no evidence of settlement at Op. 36 during the Early and Late Postclassic, both investigated buildings and nearby basins having been largely abandoned by this time.

Though almost certainly an artifact of our research strategy, settlement at Op. 36 seems to have been relatively short-lived but intense (compare the sequence with that reconstructed for neighboring Op. 12). The first recognized occupation (Late Classic I, II) is associated with a significant trash deposit and the excavation of two extensive depressions. The immediately following span (Late Classic II, III) sees the erection of four substantial edifices, though the aforementioned declivities were seemingly abandoned by this time, functioning primarily as trash containers. Late Classic III occupation is not well represented, and Op. 36 may have supported no more than a scattered population by this interval. The area was probably abandoned before the onset of the Postclassic.