UC San Diego

Caltrans, in cooperation with the Federal Highway Administration (FHW A), proposes to upgrade Highway 25, the Highway 25/101 interchange north of Hollister and south of Gilroy in San Benito and Santa Clara Counties and construct a Highway 25/156 interchange north of Hollister in San Benito County. Two related archaeological sites: the Miller Cemetery site (CA­SCl-308/H) and the Bloomfield Ranch site (CA-SCL-697H), are located in the southwest and southeast comers of the intersection of State Highways 25 and 10 I. Both sites contain historic and prehistoric components that may include human remains. The Las Animas geophysical study was carried out near the intersection of state Highways 25 and 101. This study was conducted to identify the locations for the Mariano Castro adobe foundations, the Henry Miller house foundations, and other historic and prehistoric features including hwnan burials in compliance with 36 CFR Part 800. This survey was designed to employ geophysical techniques that included three technical approaches: ground penetrating radar (GPR), total field magnetometry (MAG), and electromagnetic induction (EM). Only two of the geophysical tools were used, EM and GPR. Upon inspecting these locations, it was decided that MAG would not be effective because of the high metal content of the proposed survey area, and therefore it was not used. Geophysical mapping in the Las Animas study area has located possible historic features buried by as much as a meter of sediment and soil. GPR reflection profiles and time­slice maps showed the location of four possible buried features in the 12 grids of data that were collected. The most promising of these features is located in GPR Grid 1-4 (EM B5, 6, and 7), at the Miller Cemetery site. The GPR feature is well correlated with an EM anomaly, which shows lower conductivity material to the south and east of the GPR feature. This material may be melted adobe from the Mariano Castro house structure or other early 19th century historic residence and is well correlated with appropriate time period pottery sherds found by Julia Costello and excavation results referred to in her report (Costello, 2002). Another possible buried building foundation was located in GPR Grid 1-6 at the Bloomfield Ranch site, just north of the "grassy knoll" near the Miller house. Two other, less well-defined and more problematic, features are located in the depression north of the Miller house and to the east in the agricultural field. We suggest that subsurface testing is warranted at least for the Miller Cemetery Grid 1-4 anomaly and the Bloomfield Ranch Grid 1-6 anomaly to determine if they are associated with historic structures. Lower priority targets for testing are the Bloomfield Ranch Grid 1-5 and Grid 1-2. The overlay of modem objects and features at the Bloomfield Ranch house made a significant contribution to the geophysical anomalies at this site and may have obscured signatures from the older Mariano Castro adobe. On the other hand, the Miller Cemetery site is relatively less disturbed and yielded both geophysical anomalies and surface pottery that is consistent with a Spanish period occupation .