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...

After decades of fire suppression in the Sierra Nevada, a program was initiated in the late 1960's and early 1970's to restore the natural fire regime in Yosemite and Sequoia-Kings Canyon National Parks; under this program, for the past ~50 years, fires ignited by lightning have been allowed to burn. This natural experiment has afforded scientists a unique opportunity to document changes in biodiversity and the landscape's hydrological response as a result of the transition to a more natural fire regime. A recent paper in Environmental Research Communications , by Scott Stephens and his colleagues, summarizes some of the most important findings from research carried out at two field sites: the Illilouette watershed in Yosemite NP and the Sugarloaf watershed in Sequoia-Kings NP. Figure 1 of Stephens et al. (2021) showing the study areas. The first set of studies reviewed by the authors examined the relationship between fire severity and vegetation. Research in these two...

The first field-based investigation of the relationship between pre-fire tree mortality and wildfire severity in the Sierra Nevada has found a significant positive relationship between the two. The authors of this 2021 paper published in Ecological Applications , Rebecca Wayman and Hugh Safford, analyzed pre- and post-fire conditions at 180 plots spread across areas of mixed-conifer forest burnt by the 2015 Rough Fire and the 2016 Cedar Fire in the southern Sierra Nevada. For the pre-fire conditions, trees on the plots were examined for signs of infestation by bark beetles (e.g., pitch tubes, insect galleries, and boring dust), and a pre-fire mortality status was assigned to each tree with respect to the bark beetle damage. In addition, the authors also accounted for the role of other factors, such as relative humidity and topography. To quantify the fire severity at each plot, the authors relied on three metrics: (1) the amount of tree basal area killed by the fire, (2) an estimate o...

I recently published a paper, in Geology , showing that canyons in the northern Sierra Nevada are much older than previously thought. Earlier work had concluded that the big rivers in the Sierra (e.g., the South Fork of the American River) had only begun cutting their canyons in the last ~5 million years; the youthful age of the canyons was used as evidence to support the hypothesis that the range had undergone uplift around the same time period. To test this idea, I used an old mining report, published soon after the Gold Rush by Waldemar Lindgren, to locate deposits of river sediment that date from the Eocene (~35-50 million years old). Because these ancient river sediments were the source of much of the gold, their precise locations were well-described. The picture below shows an Eocene river deposit near the North Yuba River. The Lindgren report describes many sites where these ancient gravels are only 100-300 meters above the bottom of the canyons. This means that incision o...