Devil's Slide Improvement Project

Route 1 from Half Moon Bay Airport to Linda Mar Boulevard in Pacifica,

San Mateo County, California





Robert Gross, Chief
Office of Environmental Planning, South
Caltrans District 4
P.O. Box 23660
Oakland, CA 94623-0660


As explained in the Introduction (Section 1.0), this draft SEIS/R is intended to serve as both the revaluation of the original Final EIS for the Martini Creek alignment alternative and the initial NEPA evaluation of the tunnel alternative. Information contained in this section is provided to update the Affected Environment section of the 1986 FEIS. Descriptive details of the affected environment, as they relate to each impact issue, are discussed in section 5.0, Environmental Consequences and Mitigation Measures.



The project area is located in the Santa Cruz Mountains which are part of the Coast Ranges of California. Devil's Slide is a place name given to a steep, rocky coastal promontory located about midway between Montara and the Linda Mar District of Pacifica. Locally, however, Devil's Slide commonly refers to the entire stretch of rugged coastline extending north from the promontory to Point San Pedro.

San Pedro Mountain, which rises to over 305 meters (1,000 feet) in elevation about a half of a mile inland from the ocean, backs Devil's Slide to the east and marks the northern end of the larger landmass known as Montara Mountain. Montara Mountain forms the high northwest trending ridge which separates the San Mateo County coastline from San Francisco Bay.

The summit ridge of San Pedro Mountain trends west-northwest from Montara Mountain across the northern part of the proposed Martini Creek alignment. The terrain is characterized by steep, eroded slopes with natural gradients ranging between thirty and seventy percent. Deeply incised gullies drain the ridges. An old, abandoned county road and several graded fire and utility maintenance roads, as well as trails, cross San Pedro Mountain.

McNee Ranch State Park is located southeast of the tunnel alignment. The park consists of two separate parcels. The westerly parcel is bounded on the north by San Pedro Mountain, on the south by Martini Creek, on the west by Route 1, and on the east by the Caltrans right-of-way for the Martini Creek alignment project. The easterly parcel is bounded on the north by San Pedro Mountain, on the east by San Pedro Valley County Regional Park and the San Francisco State Fish and Game Refuge, on the west by the Caltrans right-of-way, and on the south by private property.

The San Andreas Fault has been a major factor in the development of the topography and soils. Soils of the northern slopes of San Pedro Mountain are mostly developed on sedimentary rocks and consist of sandy loam and silt loam surface layers over silty clay and silty clay loam subsoils. Boulders and cobbles derived from a conglomerate in the underlying geologic section are also present. Small coastal valleys occur throughout the length of the project along the major drainages within the Montara Mountain watershed. The soils in these valleys are deep and moderately well drained and have developed on low terraces and alluvial fans along the stream channels.

The climate of the project area is Mediterranean with a strong maritime influence. The winters are relatively warm with a short rainy season. Summers tend to be relatively cool and dry but subject to extended periods of coastal fog. Temperature ranges, both seasonally and diurnally, are narrow while air moisture remains relatively high. Wind is an important environmental factor on the exposed slopes of San Pedro and Montara Mountains.

Extremely dense northern coastal scrub covers most of the project vicinity, especially those portions over San Pedro Mountain and along the steeper foot slopes of Montara Mountain. This plant community is dominated by coastal sage (Artemesia californica) and coyote brush (Baccharis pilularis). Other common species include poison oak (Toxicodendron diversilobum), bush monkey flower (Diplacus aurantiacus), and California blackberry (Rubus vitifolius). Additional herbs include yarrow (Achillea millefolium v. californica), pearly everlasting (Anaphalis margaritacea), yerba buena (Satureja douglasii), coast figwort (Scrophularia californica), monardella (Monardella villosa v. franciscanum) and lizard tail (Eriophyllum staechadifolium). Small grassy openings and barren rocky areas are scattered throughout the scrub areas. The scrub extends westerly from the tunnel alignment to the cliffs above Devil's Slide, although coyote brush becomes less dominant nearer the coast. Poison oak and coastal sage dominate along the bluffs.

In addition to the northern coastal scrub community described above, the project area traverses other types of vegetation that are both natural and introduced including: aquatic sites and coastal freshwater marshes/seeps, willow riparian scrub, coastal grassland, non-native forest, and pasture/ranch uses/non-native brushland.



The socioeconomic setting described in the 1986 FEIS is still accurate, with only some minor modifications needed with regard to the population information. According to the latest U.S. Census taken in 1990, the mid-coastal area population is about 20,000, which includes 8,890 people (44%) residing in the City of Half Moon Bay, and about 10,525 people (53%) living in the neighboring, unincorporated communities (U.S. Census Bureau, 1990). Section 5.14 of this document provides more detailed socioeconomic information.



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