Development of the Truckee River terraces on the northeastern flank of the Sierra Nevada

Abstract

The distribution and elevation of the abandoned strath terraces along the Truckee River in the Carson Range on the eastern flank of the Sierra Nevada are mapped and quantified with measurements from Lidar accompanied by field survey. Each mapped strath terrace is formed by incision into the Hunter Creek Sandstone and deposition of fluvial gravel by the Truckee River. The gravel contains granitic boulders sourced from the glaciated headwaters of the Truckee >20 km upstream from the terraces and display boulders ranging from 4 to 12 m in dimension, in comparison to the <1 m dimension of boulders observed in the bedload of the modern Truckee River. Be-10 terrestrial cosmogenic nuclide (TCN) surface exposure dating places limits on the age distribution of the strath terraces. The terrace sediments are suggested to be glacial outwash deposits, temporally linked with glacial cycles, and to record an average of ~0.3 mm/a tectonic uplift with respect to the Reno Basin over the last ~350 ka. Building upon earlier studies, the observations collected here increase the number of terrace levels previously mapped along the Truckee, provide initial quantitative bounds on the age of their formation, and further point to tectonic uplift as an important component in preserving this most extensive suite of strath terraces along the eastern flank of the Sierra Nevada.