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Geologic Safety Committee approves 2026 projects; members outline neighborhood hazard booklet and planned field surveys
Summary
The Portola Valley Geologic Safety Committee approved its proposed 2026 projects and discussed creating a neighborhood geologic-hazards booklet and scheduled field surveys (magnetics, gravity, short seismic lines and lidar) to test mapped fault traces, with student observers invited.
The Portola Valley Geologic Safety Committee on an unspecified date approved its proposed projects for 2026 and discussed next steps on a neighborhood geologic-hazards booklet and associated field surveys.
During progress reports, a committee member said he has an outline for “a booklet” that would document geologic hazards for each neighborhood to accompany the evacuation map the committee published last year. Simon described recent and planned surveys over the Hawthorns and the Windy Hill/Neely property, saying the team will collect hand‑carried magnetic and gravity data, one or two very short seismic lines (hammer or a Betsy gun), and may use drone lidar. He said preliminary AeroMag results should arrive this week and field experiments were scheduled for Saturday, January 24; members were invited to observe, with shuttle access from the Roberts parking lot offered.
Simon also said students would collect magnetic data using consumer phones to demonstrate techniques and that the seismic source could be a hammer or a blank‑firing Betsy gun. He described a candidate trace that the committee believes corresponds to the mapped Berrocal (Berrocal/Berrocal) line on town maps and said the team will work with property owners if the AeroMag gradient supports extending surveys.
The committee agreed to compile existing geotechnical and hazard maps (USGS/state maps, town HALT maps and previous reports) as a starting point for the booklet and to reach out to town staff and the public‑works director for records of local flooding incidents. Members discussed using stream‑gauge records and historical flood events (noting a major 1998 storm) to inform mapped flooding and liquefaction susceptibility.
The approved 2026 work plan also includes outreach and communications tasks, with volunteers asked to supply photos and graphics for a short PowerPoint the committee will present to the Town Council on Feb. 25. The committee recorded the vote to approve the projects and moved on to new business.
