Alejandro Figueroa
June 29, 2003
Rancho del Rio
Subop: 150ZE
Excavator # L3

Introduction
I began work at the Rancho del Rio archaeological site (site 150), in structure 5, Subop 150ZE. The mound for structure 5 is the northern most mound of the main plaza, and it is the tallest mound of the site together with the mound for structure 1. We placed our excavation units according to the site grid, which was oriented off of a north-south line. This caused our excavation units to be off-angle with the structure, something we had to correct when determining any stone lines and creating any drawings of the structure.

Objectives
The two main objectives of Subop 150ZE were: (1) find a terminal ceramic deposit that would help us date structure 5; and (2) identify any surface-level activity going on in the central plaza area.

Excavations
We began by opening a 1 x 1 meter excavation unit in the southwest corner of the mound for structure 5, looking for the corner of structure 5 and any lines of stone that would help us identify the southern wall of the structure. Subsequently we expanded the first excavation unit in 1-meter lots east and south, exposing the southern most tumble and rubble that fell off of structure 5. At this point in our excavation our goal was to expose all outlying of tumble, so that we could later on remove it and move into the mound, looking for a line of stones that would indicate a wall. These first excavations only went down to 30cm below the present ground surface. Surprisingly, finds in these lots (150ZE/001-150ZE/008) were very few and were only a few sherds of pottery.

At this point we began excavation our southward trench, looking for the plaza floor. This trench began at 28m east, 12m north. Also at this time we were joined by excavator L8. This addition allowed us to work in both the trench and in the exposure of the southern edge of the mound.

Further excavation at the southern edge of the mound revealed more tumble and little artifactual evidence. We began excavating the first lot in our trench (150ZE/009) down to 50cm BGS (below ground surface) and then to 80cm BGS, where we hit sterile soil. At this point we had a more clear idea of the stratigraphy of the soil around our mound. Up to 30cm BGS finds were very scarce, with only a few stones (tumble) visible. At 30cm BGS the soil surface, texture, and color changed, becoming more mineralized, compact, and of a lighter brown color. From 30-50cm BGS finds were more varied (both ceramics and lithics) and came in larger numbers. From 50-80cm BGS the soil color and texture remained unchanged, but the depositional composition changed from containing both ceramics and lithics to only containing obsidian. Every time we found a different depositional or soil composition a new lot number was assigned.

Since we had now determined the plaza floor level to being at 30cm BGS, excavations in our southward trench continued at this depth, looking for any on-surface activity.

Excavations at the southern edge of the mound continued revealing more and more tumble. One two meters of soil had been cleared southward of the mound we began taking off the first tumbled stones and excavating down to 40cm BGS, looking for the base of the southern wall of structure 5.

In our second week of excavations a regridding of the site took place, and it revealed that some of our excavation units were off-line with the grid, especially in our southward trench. At this time excavations were stopped in order to correct this error in our lines and pits. A new lot number was assigned to any and all finds that came out of the correction area of our trench, so as to avoid any confusion.

After correcting our trench excavations focused nearer our mound. All lots that contained tumble were excavated down to 50cm BGS, which is the depth at which no more tumbled stone was found. At this point we moved closer to the mound, looking for a definite line of stones toward the center of the mound, where a line of stones would more likely be found intact. Excavations in our southward trench were for the time being halted since excavator L8 began working in Subop 150ZD.

A line of stones was finally exposed near the center of the mound. It comprised four large river cobbles with their flat sides lined up in a correct angle with the mound, and supported underneath by smaller river cobbles and pebbles. We named this wall Traca-Traca. Subsequently, we began following the wall west, looking for a possible corner. Although large, tumbled river cobbles appeared to be part of the wall, a clear continuation of the wall was not found. However, since we knew the position of the wall, we continued excavating at and behind the position of the wall so as to look for ceramics that would help us date the structure. Ceramics were found, and the structure has been dated as belonging to the Late Classic period.

Once this first objective was met, we continued following our trench south, into the middle of the plaza, excavating each pit down to 50cm BGS and assigning new lot numbers to any artifacts found at the 30-50cm depth.

At 28m east, 5m north, 30cm BGS a very large deposit of ceramics was found, laden with large pieces of carbon, some of which were taken so as to determine the date of this deposit. The sherds belonging to this deposit were very large and surprisingly very intact. We have determined this to being a midden, yet its position in the middle of the courtyard is puzzling. This was the largest deposit of ceramics at the site, its size further indicating that ceramic production took place in the site.

Future Objectives and Recommendations
Since structure 5 has already been dated, it is my recommendation that for the next season more of the structure should be exposed so as to determine its function within the site. Also, areas adjacent to the mound (especially east and west) should be excavated so as to determine any relations it might have with the other mounds surrounding the main plaza.

Regarding the main plaza, a trench should be established in its middle, re-exposing the area where the midden was found, and determining its size, so as to find out its purpose and significance.