Sierra Science Lecture Series Presents: From Mountains to Valleys: The Connection Between Groundwater and Surface-Water

March 3, 2020
The Colorado River cuts into the Redwall Formation at Vasey's Paradise
Thirty-two miles downstream from Lees Ferry, the Colorado River cuts into the Redwall Formation, exposing ancient groundwater passages. Vasey’s Paradise is one groundwater channel system that still delivers North Rim water into Grand Canyon. Photo by Gus Tolley.

Dr. Gus Tolley will present the next Sierra Science lecture; From Mountains to Valleys: The Connection between Groundwater and Surface-Water.

Although surface-water flow is relatively easy to understand since it can be physically observed, groundwater flow is much more obscure since it is practically invisible. Despite its mysterious nature, groundwater accounts for about 40–60% of our water supply. In California, groundwater aquifers can store more than 15 times the volume of all surface-water reservoirs in the state combined, making them a valuable asset during prolonged droughts. This presentation will demystify groundwater and explain how it is intimately connected to surface-water. Results from research conducted in mountainous watersheds in New Mexico and Colorado, and an alluvial groundwater basin in Northern California, are used to illustrate processes such as recharge, flow, discharge, and streamflow depletion.

The presentation will be held on Tuesday, March 10, from 6:30 p.m.-7:30 p.m., in the Multipurpose Center, building N12-103, at the Nevada County Campus. Come early and enjoy a meet-and-greet and refreshments at 6:00 p.m.

About our Speaker

Dr. Gus Tolley received a B.S. in geology from UC Santa Barbara, a M.S. in hydrology from New Mexico Institute of Mining and Technology, and a Ph.D. in hydrology from UC Davis. His doctoral research focused on groundwater-surface-water interactions in agricultural groundwater basins with groundwater dependent ecosystems. He has experience with development, sensitivity analysis, calibration, and uncertainty analysis of integrated hydrologic models. He was one of the lead developers of the Scott Valley Integrated Hydrologic Model (SVIHM), which is currently being used to formulate the groundwater sustainability plan for the basin. He recently returned to Daniel B. Stephens & Associates where he is working out of the Grass Valley Geo-Logic Associates office. 

Upcoming Presentations

  • April 14- California Invasive Species: Mussels, Rodents, Snails, and Frogs – Oh My | Dr. Heather Perry (Env Scientist, Cal Dept Fish & Wildlife) 
  • May 12- Environmental Factors Affecting Juvenile Salmonid Growth | Dr. Robert Lusardi (UC Davis Center for Watershed Sciences) 

The Sierra Science Lecture Series is presented by Sierra College Nevada County Campus and Sierra Streams Institute. 

Location and Parking

The Nevada County Campus is located at 250 Sierra College Drive, Grass Valley, CA 95945. Talks are in the Multipurpose Center Building N-12. Parking is $3, and you can purchase permits at the kiosk machine at the main entrance to the campus. For more information, contact the series coordinator, Jason Giuliani, at

About Sierra College

Sierra College District is rising to meet the needs of our community. Sierra College serves 3200 square miles of Northern CA with campuses in Roseville, Rocklin, Grass Valley, and Truckee. With approximately 125 degree and certificate programs, Sierra College is ranked first in Northern California (Sacramento north) for transfers to four year universities, offers career/technical training, and classes for upgrading job skills.  Sierra graduates can be found in businesses and industries throughout the region. More information at