Analyzing the annual maximum streamflow of the San Gregorio Creek reveals a notable correlation between heavy rain years and increased landslides in the region.

San Gregorio Creek, named after Saint Gregory, is a picturesque river in San Mateo County, California. Flowing from the rugged Santa Cruz Mountains, it winds through lush forested canyons on its southwest journey. Covering a watershed of about 61 square miles, it lies 40 miles south of San Francisco. Numerous creeks within the San Francisco Bay Area offer the potential to illustrate this straightforward connection between elevated streamflow and landslides due to their correlation with soil moisture levels.

Location of San Gregorio Creek stream guage:

The double exclamation marks signify the rain years when heightened landslide activity occurred. It's important to note that the stream guage was non-operational during the period of 1995 - 2000.

Citation:

U.S. Geological Survey, 2016, National Water Information System data available on the World Wide Web (USGS Water Data for the Nation), accessed [September 18, 2023], at URL https://waterdata.usgs.gov/nwis/inventory/?site_no=11162570&agency_cd=USGS.

Rainfall and Landslides in Northern California | U.S. Geological Survey. 2 Apr. 2019, https://www.usgs.gov/programs/landslide-hazards/science/rainfall-and-landslides-northern-california .