CONTINUING INNOVATIONS OF THE CALIFORNIA GEOLOGICAL SURVEY’S REPORTED CALIFORNIA LANDSLIDES DATABASE TO IMPROVE SITUATIONAL AWARENESS DURING STATEWIDE LANDSLIDE HAZARD EMERGENCY RESPONSE, NOVEMBER 2023 – MARCH 2024

From mid November 2023 until late March 2024, sixteen atmospheric river events impacted California, resulting in water year-to-date precipitation accumulations varying from more than 200 to 300% above average across selected areas of the state. Similar to the 2022 – 2023 winter storm season, California experienced historic flooding and multi-modal landslide activity that damaged transportation infrastructure, homes, property, and threatened life-safety and economic welfare across the state. Consequently, a state of emergency was declared by the Governor of California as well as by the President of the United States. California Geological Survey (CGS) staff worked to provide situational awareness of statewide landslide hazards to the State Geologist through partnership with various government and community sources. CGS leveraged its Reported Landslides Database (RLD) mapping tools for desktop and field surveying to rapidly identify areas of observed landslide impacts. Applying lessons learned from the 2022 – 2023 winter storm season, and in combination with development of new GIS mapping applications, CGS geologists assimilated available reported landslide data from multiple sources including, but not limited to: photos and event timing information from crowd-sourced reporting (e.g., X, Facebook), local news media sources, state, county, and municipal agency reporting, California Highway Patrol (CHP) data, National Weather Service (NWS) data, and review of firsthand reports provided by the public. The RLD mapping team identified at least 600 landslides, resulting in deployment of field teams to provide further assistance to hardest hit areas. CGS utilized these data to guide ongoing support of partner agency response to landslide hazards statewide.