Buried Deposits - Baja and California

Strategies for inventorying and evaluating archaeological resources in the San Diego region are commonly based on the assumptions that substantial cultural deposits will be manifested on the present ground surface and that excavation to sterile soil will determine the lower limits of the deposits. However, buried sites or buried components also exist. G. Timothy Gross and Mary Robbins-Wade (2008) discussed the circumstances under which archaeological deposits have been buried in western San Diego County, along with examples of the discovery of such deposits.

Buried deposits have been documented in such settings as coastal marshes, river floodplains, alluvial fans, and areas of aeolian deposition. The thickness of the culturally sterile overburden has varied from a few tens of centimeters to as much as several meters. Prehistoric cultural deposits are also often buried as a result of modern construction or dumping. A key requirement for the natural burial of cultural deposits to occur seems to be that the rate of sedimentary buildup must be relatively rapid. Another factor in burial may be only a limited amount of bioturbation by ground squirrels and gophers, which would otherwise often bring evidence of cultural deposits to the surface, or which would obliterate culturally sterile strata within multicomponent sites.

Buried deposits have been discovered in several different ways. Some have been seen in the profiles of natural exposures that were created by stream or coastal erosion. Others have been detected during grading or trenching for development projects. Still others have been found through purposeful programs of archaeological testing, by means of coring, mechanical trenching, or hand excavation through deposits that lacked evidence from any underlying cultural deposits but that were considered likely candidates to conceal such deposits based on their general location and geomorphic circumstances.

Examples of buried deposits reported in the San Diego region, many of them cited by Gross and Robbins-Wade (2008), include:

SDM-W-80, SDM-W-87, SDM-W-127, SDM-W-159, and SDM-W-166. These sites, buried by coastal sand dunes along the San Diego coast between Point Loma and Agua Hedionda Lagoon, were recorded by Malcolm J. Rogers in notes on file at the San Diego Museum of Man. The covering aeolian deposits were described as “shallow” at W-159 and as 30 centimeters thick at W-87.
SDM-W-123. Of middle Archaic age, the Kelley Spring Site was described by Rogers as a “slough margin midden in a lateral canyon.” The site’s 120-centimeter-thick deposit of shell midden was interbedded with sands and lay under 20-30 centimeters of apparently sterile alluvial sediments.
SDI-10,669. According to Gross, site records for several small sites in the floodplain of the Tijuana River have been suggested as portions of an ethnohistorically recorded Kumeyaay village, Millejo. However, no surface evidence for a large site in this vicinity has been reported. Florence Shipek (1976) suggested that the village site may have been buried by sediment during the extensive flooding of the river in 1895 and 1916.
SDI-12,455 and SDI-12,456. Two prehistoric camp sites in the Tijuana Slough lie on silts that were buried by sands of apparently aeolian origin (Alter et al. 1991). Flooding has partially eroded the sands and re-exposed the cultural deposits.
SDI-7455. Monitoring and systematic coring for the Otay River Pump Station project identified a substantial buried extension of this previously recorded site, located near the southeastern margin of San Diego Bay (Andrews 2003). Several distinct strata of relevance to the cultural deposit were observed: Stratum A, consisting of about 100 centimeters of modern fill; Stratum B, with river channel and levee deposits, about 50-70 centimeters thick, overlying the cultural deposits; Stratum D, a Late Prehistoric cultural component, about 80 centimeters thick; Stratum E, consisting of 40-200 centimeters of river levee alluvium; Stratum F, another Late Prehistoric cultural deposit, about 150-300 centimeters thick; and Stratum G, a middle Holocene cultural deposit about 30-70 centimeters thick.
SDI-4644. The Edgemere Avenue Site is located in the floodplain of the Sweetwater River, approximately 3 kilometers east of San Diego Bay. The site was not identified during a surface survey, but was exposed in a temporary flood control channel (Leach 1975). The upper 40 centimeters of the deposit, with bioturbation and historic-period disturbance, contained meager amounts of cultural material. Underneath that, extending between 40 and 80 centimeters below the ground surface, was the main cultural deposit, including a living floor.
SDM-W-162. This site consists of an array of middens exposed by the erosion of sea cliffs, on southwestern Point Loma (Rogers’s notes). From 30 to 210 centimeters of deposits laid down by “outwash” had buried the middens, the largest of which was 80 centimeters thick.
SDI-14,152. The Heron Site, a Late Prehistoric campsite, was located on the bank of the San Diego River in Mission Valley. It was discovered during the excavation of a pond in the river’s bed, as part of a wetlands rehabilitation project (Schaefer et al. 1996). More than 300 centimeters of alluvial sand and recent historic fill had buried the prehistoric cultural deposit, which lay below the normal water table. The site was only discovered because construction monitoring occurred at the end of a very dry season.
SDI-4513 and others. Ystagua, an historically documented Kumeyaay village also containing a middle Holocene component, is located in Peñasquitos valley, in settings that include hilltop, slope, and floodplain. Numerous studies have been conducted at different portions of the site (see Gallegos et al. 1989 for an overview). At a location near the base of a slope, cultural deposits extending to a depth of 250 centimeters were observed to be interrupted by sterile layers of sand and cobbles. Some of the archaeological investigations stopped at the sterile deposits and failed to detect lower components (Hector 1988; Hector and Wade 1986; see also Carrico and Gallegos 1988).
SDI-4629. The large, middle Holocene Roaring Brook Site is located on an alluvial fan adjacent to the northern shore of Peñasquitos Lagoon. Several loci were evident on the surface of the site, but additional loci were discovered buried beneath 90-370 centimeters of sediments (Smith and Moriarty 1985b). Shell lenses within some loci were also found to be separated by culturally sterile layers.
SDI-149. The C. W. Harris Site, located adjacent to the San Dieguito River, contained Late Prehistoric artifacts on its surface (Warren 1966; Warren and True 1961). However, it also had early Holocene cultural deposits that underlay sterile or nearly sterile alluvial strata.
SDM-W-105. This site, located in an alluvial fan on the southern margin of Batiquitos Lagoon, was reported by Malcolm J. Rogers as being buried under 46 centimeters of outwash. The middle Holocene cultural deposits, with a total thickness of 120 centimeters, were interbedded with sterile sands.
SDI-811 and SDI-812/H. These sites are located in the lower floodplain of Las Flores Creek, on Camp Pendleton (Reddy 2005). A large Late Prehistoric component was observed in the upper 70 centimeters of the SDI-811 deposit, but middle Holocene components that extend as deep as 660 centimeters below the surface were found to underlie noncultural strata formed by braided stream and channel sand deposits.
SDI-8435. The Patterson Site is situated on the west bank of San Mateo Creek, on Camp Pendleton. On the surface, only a single flake was found, although visibility was hindered by dense vegetation (Hines and Rivers 1991). Two thin bands of habitation debris were found buried under 80-100 centimeters of alluvium. Soil development and the presence of flexed burials suggested that the deposit predated the Late Prehistoric period.

PROSPECTS

Future archaeological investigations may be able to clarify the probability of buried cultural deposits under a variety of circumstances, and refine the strategies and methods available for discovering them.