Analyzing the fossils
(page 2 of 3)
Each day, Sarah set out with the appropriate locality maps in hand, information on her targeted
localities, a GPS unit supplied by the Park, collecting bags, lunch, and lots of water. After about
eight hours of bushwhacking, climbing, and crawling over the mountain each day, the next task was
to document, interpret, and compare the findings with past records. In total, Sarah was able to
locate 51 of the original localities and identify five additional sites. Many of the historical
records she was using were incomplete and often difficult to interpret. Without the current
understanding of plate tectonics and todayís technology, it is not surprising to find that
there were numerous inaccuracies in much of the earlier work. In some cases, a single geologic
formation had as many as three different names in as many publications. In others, that same
formation was assigned to the Miocene in one report, while another report listed it as Oligocene.
Much of the rationale for the name and age assignments was based on correlation with geologic
units and fossil finds in other parts of the state. So as new evidence was found, dates and names of units fluctuated.
Without an established state standard to follow, Sarah based the fossil resource management plan on the geologic formations, evaluating each for its level of exposure and fossil content. Now, this resource management plan, as well as the criteria used to generate it, may become the state standard.
A rock sample (top) from an exposure (bottom; see arrow) of the Mt. Diablo Ophiolite Formation, a mixture of oceanic and island arc components dating from the Jurassic Period. (photo by Sarah Rieboldt)