Here are two well-exposed and prominent rhyolite volcanic "plugs" in the Lower Miocene Valley Springs Formation, Ione Basin, western foothills of the Sierra Nevada, Amador County, California. Paleobotanist Howard Schorn, geologist Robinson Cecil and I passed this dramatic outcropping on our way to the type locality of the Valley Springs Formation near Valley Springs, Calaveras County, California. Image taken on June 3, 2003.
In the Valley Springs area of Calaveras County, Howard drove geologist Robinson and me to the type locality of the Lower Miocene Valley Springs Formation--which lies along the flanks of a prominent peak a few miles northeast of town. The formation is unfossiliferous here, although, fortunately, a couple of localities in the dominantly rhyolitic terrain have yielded to paleobotanists a rather sparse, yet invaluable fossil flora. The Valley Springs overlies the Middle Eocene Ione Formation in disconformable fashion throughout the Ione Basin--that is, there was no sedimentary deposition between the end of Ione times, roughly 45 million years ago, and the beginning of the dominantly volcanic, rhyolitic sandstones which characterize the Valley Springs Formation, approximately 23 million years ago.
We lunched in the small community of Valley Springs at a sandwich shop along main street--then decided to head north to the famous Lygodium Gulch fossil leaf locality in the Ione Formation--a site Howard and I first quarried during our field trip of July 27-August 2, 2002; a second visit by student collecting crews from a Community College and a university on October 26-27, 2002 had produced additional quality fossil leaf specimens, now housed in the archival paleobotany collections at the University California Museum Of Paleontology in Berkeley; the collections from the Ione await paleobotanist Dr. Jack A. Wolfe's world-famous CLAMP analysis (Climate Leaf Analysis Multivariate Program), in which the overall shapes, sizes, and margins of the leaves are studied to determine the paleoelevations and paleoclimate of a specific fossil flora.
Please note: All fossil localities in the Ione Formation of Amador County, California, presently occur on private property; explicit permission from the land owners must be secured before collecting fossils there.