A River Runs through It—Geology along the Truckee River Valley from Reno to Pyramid Lake
Authors: Rich D. Koehler, Andrew V. Zuza, and James E. Faulds
Series: Educational Series 59
Format: 19 pages, color
Major stops on this field trip include the following:
- A “young” one-million-year-old lava that flowed into the Truckee River Canyon
- Paleo–Lake Lahontan sediments from glacial times
- Several major earthquake faults
- Tufa mounds
- Fossil locality with 15-million-year-old leaf imprints
This field trip follows the route of the Truckee River canyon from Reno to its terminus at Pyramid Lake (figure 1). From Pyramid Lake, the trip then continues southwest across the Virginia Mountains and south through Warm Springs and Spanish Springs valleys back to Reno.
The Truckee River is sourced from Lake Tahoe at an elevation of 6,233 ft (1,900 m) in the Sierra Nevada and flows 121 miles (195 km) to its terminus at the southern end of Pyramid Lake at elevation 3,793 ft (1,156 m). The river’s drainage basin encompasses around 3,060 sq. mi. (7,925 km2) and gets its name from the Paiute chief, Truckee. The Truckee River is the main source for agriculture irrigation and residential water needs in the Reno region and is susceptible to extreme flooding, especially during heavy winter rain storms. As a result, the flow of the river is regulated by a series of dams east of Truckee, California, including Boca Reservoir, Stampede Reservoir, Prosser Creek Reservoir, and Martis Creek Reservoir. Water transmission flumes line the upper part of the river and are susceptible to damage from rock fall and strong ground shaking during local earthquakes.
Many historic floods have affected the Truckee Meadows (Reno basin) area, including major events in 1862, 1875, 1890, 1904, 1907, 1928, 1937, 1943, 1950, 1955, 1963, 1986, and 1997. The devastating “New Year’s flood” of 1997 caused over 450 million dollars in damage and closed downtown businesses for weeks (figure 2). This event was caused by a phenomena known as the “Pineapple Express” in which several warm storms from the Hawaiian Islands produced heavy rainfall in the Sierras, saturating and melting the snow pack and resulting in flows around 18,000 cfs.
The trip discusses historic flooding history, paleo–Lake Lahontan timing and stratigraphy, the connection of Pyramid Lake to Lake Lahontan, Neogene tectonics and paleovalley offsets, recent tectonics and earthquake hazards, and bedrock geology. At stop 6, there is an opportunity to hunt for macroscopic fossils preserved in 15-million-year-old diatomite.
NBMG coordinates annual geology field trips for the public during Earth Science Week. These field trips are fun, educational, family oriented, and always free. NBMG has been an active participant in Earth Science Week since it began in 1998.