But it does not, by itself, tell you whether the bone was deposited in the stratum where it was found at the time the animal died or whether it was reworked — moved by water, soil creep, or other processes into a stratum of different age.

The possibility of reworking is a standard concern in archaeology and geology, and for a find as significant as Arlington Springs, it had to be addressed.

The geological and chronostratigraphic work — led by Johnson in collaboration with specialists from San Diego State University and other institutions — involved relocating the specific sedimentary unit at Arlington Canyon from which the femora had eroded, mapping its lithological characteristics, and independently dating multiple materials from it and from overlying and underlying units.

The character of the sediments was itself informative.