20 May 2025, Benton Range, California

All is well at the SEOE Geology Field Camp. Today only marks our sixth day of field camp, yet it feels like we have already accomplished so much. Having started in a developed campground for the first three nights outside Napa, California, we have successfully transitioned to primitive camping, and have settled into our system of self-sufficiency that we will employ until our penultimate camp in Colorado in a few weeks. The students have completed a project involving the creation of unit descriptions for a wide range of rock types and compiling a regional geologic interpretation, and have become fully accustomed to — and seem to be embracing — the mobile field camp life. The stunning landscapes, geology, and weather have helped.

Class photo from Point Bonita, California with San Francisco in the background.

This morning the students are wrapping up their first mapping project in some intrusive rocks in the Benton Range tucked between the eastern side of the Sierra Nevada and the White-Inyo Mountains along the California-Nevada border. This afternoon we will head to Chalfant quarry to see a classic exposure of the Bishop Tuff which, 765 thousand years ago erupted for six days from the Long Valley Caldera just to our northwest, spreading ash and a pyroclastic flow locally, with ash traveling as far east as Kansas. In total more than 600 cubic km of material were erupted, forming one of the largest calderas on Earth. That is hard to fathom (Mt St Helens erupted about one cubic km of material).

SEOE geology field camp students map cross-cutting dikes in the Benton Range, California.

This year, because of successful fundraising over the past few years — thank you! — and a small cohort, we are doing a complete transect of the North American Cordillera at the latitude of ~39° N: roughly from the Franciscan complex along the Pacific Ocean in Marin County, California, to the eastern Rockies near Colorado Springs, Colorado. We aspire to study all of the major belts involved in this classic subduction-related orogen with the goal of developing our students’ ‘big-picture’ integrative skills along with the conventional skills learned at field camp. So far so good — the students have done an impressive job of tying together seemingly disparate observations, less than one week in.

Having sent our loaded cargo truck — The Badger — westward a week earlier with two graduate student staff, the rest of our journey began inauspiciously with a delayed flight out of Columbia due to mechanical issues, despite it being the first flight of the day. It led us to missing our connecting flight in Dallas, but we were able to get on flights through Denver to Sacramento, where the ground portion of field camp would begin. (Incidentally our flight from Denver to Sacramento flew over or within sight of nearly all our project areas, so that is a silver lining). More than an hour delay on the tarmac for thunderstorms in Denver got us to camp on the shores of Lake Berryessa after dark, some 21 hours after we awoke at 3 AM Eastern. Suffice it to say that this field camp director was concerned about getting off on the wrong foot, and losing the students so early in the course. I for one was exhausted.

Fortunately, spectacular geology and landscapes in the Marin Headlands and at Ring Mountain on the Tiburon Peninsula quickly turned things around on Thursday May 15, the first full day of geology. We were able to observe all of the major elements of the complicated Franciscan assemblage that forms much of the Coast Ranges of northern and central California. Students observed and described immature litharenites, deformed bedded chert at Rodeo Cove, pillow basalts at Point Bonita, and blueschists, eclogites and amphibolites at Ring Mountain.

Protoprof and Field Camp Manager Lance Tully guides students through a unit description of litharenites in the Franciscan complex at Rodeo Cove, California.

Friday May 16 saw us moving inland to examine the Jurassic and Cretaceous Great Valley Sequence that represents the onset of the Central Valley that is so critically important to American agriculture and providing for our residents. One of the most meaningful aspects of this career is watching students realize how significant geologic processes are in influencing — if not defining — societal, political and economic landscapes, amongst many other things.

Field camp students examine classic turbidites of the Great Valley Sequence near Monticello Dam in the California Coast Ranges.

Saturday May 17 involved the first breakdown and relocation of camp as we proceeded eastward across the Central Valley and up the western slope of the Sierra Nevada, where we stopped to examine and discuss the implication of gold-bearing fluvial placer conglomerates deposited on the western slope some 40 million years ago. Whereas our primary focus was on what such deposits mean for the magmatic, geodynamic and landscape processes of the Sierra, it was meaningful to discuss what these deposits also meant for the development of the United States. Gold from Sierran hydrothermal deposits were concentrated in these ancient river deposits and subsequently released into modern streams where prospectors located them in the late 1840s, spawning the Gold Rush that transformed California into the economic powerhouse — for good or for bad — that has fundamentally transformed American and global life. With no Gold Rush, there would be no Silicon Valley, and all that it involves. Again, geology has an outsized influence on humanity.

SEOE geology field campers examine the classic Eocene auriferous gravels of the western slope of the Sierra Nevada that instigated the California Gold Rush, transforming the United States.

We continued up the western slope arriving at Donner Pass just in time to examine classic Sierran granitoids and their volcanic carapace as a hypothermia-threatening sleet and rainstorm inundated us. In their second test of willpower, the students persevered enabling us to wrap up an understanding of the tectonic, magmatic and geomorphic processes at work in creating the ‘California triad’ of the Franciscan, Great Valley and Sierra Nevada complexes, that were so influential in the formation of the geology will we see across the Great Basin, into the Colorado Plateau and the Rockies in the coming weeks. (I hope I am not giving too much away for any students reading this!).

Field camp examined the tonalites and mafic enclaves of the Sierra Nevada batholith at Donner Pass just as a sleet storm arrived.

We descended down through Truckee into the Reno-Tahoe area where after a quick resupply we bedded down for the night on the hills below Peavine Peak before our trip down to the eastern Sierra the following day. With casual but informative stops at Lake Tahoe, Mono Lake, and the eastern brethren of Yosemite Valley, we took in views and perspectives of (fresh and saline) endorheic lakes and basins and what they mean for tourism, migratory birds, ecology, and late 1980s hair-rock videos.

Once we wrap up things here in the Benton Range and Owens Valley region, we are off to desolately beautiful central Nevada to examine the myriad processes of the Cordilleran system captured by the Great Basin. I look forward to watching the students connect some very different geology to what they have seen in California so far. Onward.