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San Mateo County Profile 4.2 PHYSICAL SETTING 4.2.1 Geography and Topography The Santa Cruz Mountain range bisects San Mateo County, essentially creating three regions:  The Bayside largely consist of mudflats, marshes, artificial fill, and broad, flat alluvial plains. The low- lying Bayside region gradually increases in slope toward the Santa Cruz Mountains, eventually becoming rolling foothills. The San Andreas Fault parallels the Santa Cruz Mountain range, delineating the threshold of the Bayside and beginning of the Santa Cruz mountainside.  The Santa Cruz Mountains are generally rugged with dense forest and steep slopes, often exceeding 50 percent. This area is characterized by large amounts of open space, recreational areas, and trails, including Wunderlich Park, Huddart Park, and the Fifield-Cahill Ridge Trail.  The Coast-side of San Mateo County consists of sloping foothills of the Santa Cruz Mountains to nearly sea-level coastal terraces along the Pacific Ocean. The difference in topography along the coastline itself ranges from wide, sandy beaches to rocky coves. In some places, high, rocky cliffs have emerged from the gradual erosion of coastal terraces. Elevation ranges from sea level along the coast and bay to 2,572 feet above sea level at the Santa Cruz Mountains. 4.2.2 Natural Resources San Mateo County’s natural resources range from forested mountains to bayside marshlands and coastal ecosystems. These natural resources face pressure from development, invasive species, natural hazards, and climate change. The Bay Area is home to 35 species protected under the Endangered Species Act (Center for Biological Diversity, 2021). These resources are an integral part of the economy, sense of place, and traditional culture of the island communities. They need to be considered in hazard mitigation planning, because they are affected by natural hazards and can influence the way that hazards alter the built environment. 4.2.3 Water Resources The bayside of San Mateo County has experienced high amounts of urban development, which required flood control modifications within nearby watersheds. Streams that once naturally flooded and meandered around hillsides before reaching the San Francisco Bay were hardscaped and straightened into channels. However, the coast side of San Mateo County consists mostly of open space and agricultural land with sparsely distributed towns. Most watersheds on the coast side have little to no flood control modifications; however, water diversions, lack of riparian zone management, and water quality issues all present challenges for these resources. There are nine major watersheds in San Mateo County (County of San Mateo Public Works, 2021):  Gazos Creek Watershed—Gazos Creek is a priority watershed for steelhead and coho salmon recovery. Major tributaries include Old Woman’s Creek and Middle Fork Gazos Creek.  Pilarcitos Creek Watershed—Major tributaries include Arroyo Leon and Mills Creek. The San Francisco Public Utilities Commission manages the Pilarcitos Reservoir in the upper watershed.  Pescadero Creek Watershed—The Pescadero Creek Watershed is the largest watershed in San Mateo County. It consists of two major sub-watersheds: Pescadero Creek and Butano Creek. The watershed also contains an impressive marsh inhabited by several native and protected species such as steelhead, California red-legged frog, and San Francisco garter snake. 4-3