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Our geocaravan left CSUN and drove north along I-5 and highway 99 to Merced where we stopped for lunch. Along the way we learned about the geology of the Ridge Basin, San Andreas Fault, Wheeler Ridge, and the southern Sierra. After lunch we drove north into the Sierra foothills past isolated outcrops of tombstone rocks (Jurassic metavolcanics) amid grasses and isolated oak trees. Three miles southwest of Jamestown we reached the Mother Lode highway named for the 49ers. To the west was Table Mountain, composed of latite that filled an ancient river valley but as the surrounding rocks eroded away now forms a prominent sinuous ridge. After a brief stop at the Glory Hole shopping center we headed for the Stanislaus River and an impressive road cut exposing the Calaveras Complex. While there Robinson Cecil, Dick Heermance, and Doug Yule presented a geologic overview of the Sierra Nevada batholith, accreted terrains, and the Mother Lode Belt. Then it was time for a refreshing dip in the old swimming hole followed by camp setup and dinner at the New Melones Reservoir. (Click on photos for additional images.)
Some of us awoke to a pungent aroma wafting through the morning air. We soon learned that one of the dogs had tangled with a skunk during the night. So as some of us had breakfast it was bath time for Henry and Pima. After breakfast we packed and headed out. The first stop was in Coloma to see a replica of Sutter’s Mill. This was the 1848 gold discovery site that changed the course of California history. Then it was on to the Empire Mine State Historic Park in Grass Valley for a tour of one of the oldest, largest, and most successful gold mining operations in the Mother Lode. After the hard rock mining tour we went to look at the results of hydrolic gold mining at Malakoff Diggins.
At Malakoff Diggins placer gold was extracted from paleochannels composed mainly of Eocene fluvial gravels using powerful streams of water concentrated by giant nozzles. Robinson Cecil, Dick Heermance, and Doug Yule discussed the Cenozoic tectonic and geomorphic evolution of the northern Sierra Nevada including: paleotopography, exhumation, low-temperature thermochronometric data, stable isotope geochemistry, paleoaltimetric studies, and detrital zircon U-Pb and (U-Th)/He ages. We then hiked into the Diggins where we saw one of the giant monitors, the colorful eroded cliffs, and auriferous Eocene gravels. We made a brief stop in North Bloomfield then got on Highway 49 and headed for Sierra Buttes and Packsaddle Camp.
After breakfast we gathered around some boulders in the campground and determined that they were glacial erratics. At that point Dick Heermance provided us with some glacial terminology, theory, dating techniques, and a history of glaciation in the Sierra Nevada. We then went on a hike to Big Bear, Little Bear, Cub, and Long Lakes. Near Long Lake we had an engaging geological discussion. Dick Heermance continued with his glaciation discussion focusing on what is known about the Sierra Buttes. Elena Miranda and Josh Schwartz enriched the discussion with their knowledge about metamorphism. Doug Yule discussed aspects of rock alteration. And Robinson Cecil spoke about the geology of the Mother Lode.
After our hike we drove to Graeagle and had lunch. This was the farthest north location on the trip. We then headed south to Lake Tahoe where we stopped at Sugar Pine Point. There Doug Yule told us about how the San Andreas fault system is getting clogged by the Big Bend in southern California and that some of the plate motion is being transferred to the Walker Lane faults via the Eastern California shear zone, Owens Valley and Death Valley systems, and the Tahoe-Sierra frontal fault zone. We learned about the active faults crossing Lake Tahoe basin and the possibility of tsunami hazards there. Our next stop was our campsite at Grover Hot Springs.
After breaking camp and taking the group photo we walked to the hot springs and talked about the mineral water content and a fault that crosses the meadow. Next we headed south over Monitor Pass and dropped down into the Bridgeport Basin and south on highway 395. We passed Mono Lake and Mono Craters and stopped at Convict Lake. Robinson Cecil reviewed our route, summarized the geology that we had seen, and pointed out some of the features around Convict Lake. Dick Heermance, while standing on a moraine, described the glacial geology of the eastern Sierra.