The Sierra Nevada Files

A paper written by one of my graduate students, Christina Tipp, has provided strong evidence that large swaths of the northern Sierra Nevada were completely buried by river sediments in the Eocene, ~30-40 million years ago. This study, published in the American Journal of Science , presents our first glimpse of the northern Sierran landscape in the Eocene and early Oligocene. Known as the 'auriferous gravels' or the 'Tertiary gravels,' these ancient fluvial sediments contained gold that was sought after by miners during California's Gold Rush. At the peak of the Gold Rush, the loosely cemented deposits were blasted by water cannons known as monitors and funneled into sluice boxes to recover the gold in a process called hydraulic mining. Hydraulic mining at the Malakoff Diggings, just north of the South Yuba River. The cliffs in the image are composed of ~40 million year old river deposits. Note people in the lower left of the image for scale. Photo credit: Universit

Plants rely on rainfall and groundwater to stay alive, with the relative proportion of each varying according to different factors such as rainfall seasonality and rooting depth. In periods of drought, plants must increase their dependency on groundwater; however, not all groundwater is the same. Some groundwater systems are recharged by recent precipitation, while others continue to transmit water from storms that happened several decades or even centuries in the past. In a 2021 paper published in Environmental Research Letters, Zach Meyers and his colleagues sought to answer an important question: do plants nourished by old groundwater do better than those dependent on young groundwater? They hypothesized that the former would do better during periods of drought because the old groundwater source would be less affected by the current climatic conditions and, thus, would vary less and be more consistent. From 2011-2017 California experienced its worst 6-year drought on record, prov