San Mateo's History of Fire
Fire has shaped the Santa Cruz Mountains for millennia. What changed is not the fire, it is the fuel that a century of suppression allowed to build, and the tens of thousands of homes we placed in it. In 2020, the CZU Lightning Complex ended any doubt about whether large fire could reach San Mateo County.
A Fire-Adapted Landscape
The Santa Cruz Mountains' topography, fuels (forest, chaparral, and grassland), and weather make them conducive to periodic large fires. Historically the range burned on a roughly decadal basis, creating a patchwork of burned and unburned areas. Indigenous peoples burned the landscape deliberately for millennia. Before European settlement, frequent smaller fires consumed forest understory while leaving old-growth redwoods standing, and kept shrubs and Douglas-fir from encroaching on grasslands.
A century of fire suppression, the introduction of invasive plants, and limited forest management reversed that pattern. The result is uncharacteristically heavy fuel loads across much of the county, with homes built among them.
"Since the 1970s, there has been increasing public pressure to preserve local natural features. This philosophy has influenced the management of parks, open space, and private land holdings. The result is an ever-increasing land base that is often void of disturbance, whether by wildfire or resource harvesting. In many instances, the resulting landscape is overgrown with a variety of species in a variety of different age classes. The proximity of homes to flammable landscapes can be a potentially dangerous situation in the event of a fire."
The CZU Lightning Complex, 2020
For decades, San Mateo County's fire record looked deceptively quiet. Most local fires stayed under an acre thanks to early detection, aggressive suppression, and favorable weather, and the largest recent event was the 50-acre Skeggs Fire in 2017. Fire professionals kept repeating that a large fire here was a matter of when, not if.
When came on August 16, 2020. Lightning from a dry storm ignited fires that merged into the CZU Lightning Complex, which burned 86,509 acres across San Mateo and Santa Cruz Counties over five weeks, destroyed nearly 1,500 structures, forced the evacuation of tens of thousands of residents, and killed one person. In San Mateo County the fire burned through the Butano and Pescadero Creek watersheds and threatened coastside communities. Most of the structure loss occurred in the intermix communities of the Santa Cruz County side, where homes scattered through heavy fuels ignited faster than any suppression force could protect them.
The CZU fire confirmed what post-fire research across California has shown: outcomes were driven by ember exposure, near-home fuels, and building vulnerability. It also demonstrated the limits of suppression. At the fire's peak, resources were spread across hundreds of simultaneous lightning fires statewide, and many communities faced the fire with no engine in the driveway. What a household had done before the fire was what protected it.
What History Tells Us to Do
The lesson of local fire history is not that the mountains will burn, though they will. It is that the condition of our parcels and neighborhoods when fire arrives determines the outcome. That means defensible space and home hardening at the parcel scale, fuel reduction and coordination at the neighborhood scale, and support for the fuel management and prescribed fire work that is slowly returning beneficial fire to the landscape.
