Excavation began in November 1964 close to the site of the original cut bank exposing siliceous material. Twenty-two pits and trenches had been dug by 1980, most of them between 1964 and 1972. Artifacts have been recovered from three Master Pits and associated trenches. Most significantly, Control Pits dug on the higher portion of the Yermo Fan have produced a vast quantity of fractured rock, but no identifiable artifacts.
All digging has been accomplished with small hand implements: dental picks, awls, hammers, and chisels, etc. The deposit, much of it cemented to rock-like hardness, has been removed under tight controls, three inches at a time, to a depth of about 30 ft (9 m). In some sectors this is deep enough to expose the Barstow Formation beneath the Yermo Fan. All rocks (modified and unmodified) are left in place until related levels are finished–then all are plotted, triangulated, recorded, and photographed before removal. Only small tools and flakes that could not be so identified until cleaned were recovered by screening. These are the only items not photographed in place. Pedestaled specimens may be undercut and a mirror placed under the object, permitting a photograph to reveal both sides of the object while it is still in place. While Dr. Leakey was alive, most of the prime tools were left in place for him to see.
Measurements in Master Pit I have been established by the use of an overhead bridge from which a calibrated chain is dropped to establish depths and accurately determine grid corners. According to Leakey and Simpson’s plan, all pits and trenches were dug under a single grid location system. Thus, Master Pit I was started by numbering the northwest 5 x 5 ft square as P-19 rather than the usual A-1. In so doing, excavations could be extended in any direction, with section coordinates specified by west-to-east letter designations and north-to-south number references.
Once out of the pit, a specimen is recorded in the field laboratory. Then it is boxed by section and level. Those objects regarded as most significant by Leakey went to artist Austin Dennison for casting. Statistical work, done in the early stages by Mr Dennison and his wife Dorothy, concentrated on distribution charts and graphs, soils analysis, and comparative rock counts. An important aspect is the ratio of non-siliceous (mainly volcanic) rock to siliceous rock. This is taken at every three-inch level. In upper levels, the ratio was high (over 5:1); in the deeper levels it became much lower (2:1 or less).
After the statistical data is obtained, the non-artifact rock material is stockpiled in sequence, where it is available for further study. Objects identified as artifacts are archived at the San Bernardino County Museum in the city of Redlands, some 90 miles (145 km) from the dig.
Each quarter “The Calico Report” (formerly “Friends of Calico Newsletter”) chronicles ongoing developments at the site, along with special topics such as analyses of the lithic material and related archaeological sites in a variety of geographic locations. Work at the dig is supervised by Fred E. Budinger, Jr., Calico Project Director, who has been in the forefront of the site’s development for more than 25 years.