1999 Field Season: Day 25

July 19, 1999

Several teams of three were assigned to dig geologic trenches today as part of our continuing effort to understand in detail the structural and sedimentary history of the Olorgesailie Basin. While our excavation trenches tend not to be very deep (we try to dig through the least amount of overburden as possible), geologic trenches often climb the entire hillside, and we try to pick the tallest slopes that will crosscut the most amount of sediment. Also, while excavation trench sizes (length and width) are determined by the distribution of fossils and artifacts within the site (the Elephant Site, with its nine extensions, is now about a hundred square meters), geologic trenches are usually only a meter to a meter and a half wide. Thus they resemble knife cuts going straight up the hillside. We are interested primarily in the sediment layers of Members 7 through 10 this season, a complex series of events starting around 780,000 years ago, that have bearing on many of the sites we are currently excavating, and have on our list to do in the near future.

A geological trench site.
Setting up a geological trench.

Work also continued on the Member 11 sites A11-10 and 15. The "C" sand layer at Site A11-10 is yielding many tools and fragments of bone and tooth. A partial lower jaw of a large antelope or horse was uncovered this afternoon. Additional clusters of stone tools are being uncovered, making the excavation crowded with specimens. We are going to have to lift at this site tomorrow. An advance crew went to the site this afternoon to place a new datum for removing the artifacts. Because of the geometry of the site, we had to place the datum within the boundary of the old excavation. Normally we wouldn't have wanted to do this, but there was no other way to see the entire excavation from a single transit position. After we were done setting the new datum, and had verified its position on the coordinate grid, we did a little numbering of the artifacts and bones to get a head start. We got through 134 specimens before the light gave out, and we were not even a quarter of the way done.

Bright and early tomorrow for the lift.

A partial lower jaw at A11-10.
Dr. Rick Potts and two transit team members.

A Final Word From Our Team