Peninsula Trails. Jean Rusmore
The Santa Cruz Mountains are part of the Coast Ranges of California. They run northwest to southeast, extending from Montara Mountain near San Francisco to Mt. Madonna near Watsonville. A natural divide splits the range into two parts at the Highway 17 pass between Los Gatos and Santa Cruz. The Spaniards called the southern section the Sierra Azul (“blue mountains”) and the northern part, the Sierra Morena (brown or dark mountains). The area covered by this guide centers on the Sierra Morena and includes land from the San Francisco Bay on the east to the Pacific Ocean on the west. The highest mountain in the Sierra Morena, at 2800 feet, is appropriately called Black Mountain.
The east side of the Santa Cruz Mountains, steeper than the west, is cut into deep canyons by streams that empty into San Francisco Bay. The upper reaches of these creeks, which still flow more or less untrammeled down through the mountains and the foothills, are some of the main delights of the mountainside parks. Where these creeks meandered across the Bay plain, they were once the dominant features of the landscape, bordered by huge oaks, bays, alders, and sycamores. Now they have all but disappeared from sight in the flatlands, being mostly confined to concrete ditches and culverts and bordered by chain-link fences. Two happy exceptions are the lower reaches of Los Trancos and San Francisquito creeks, which still retain their parklike tree borders as they wind through Portola Valley and the undeveloped lands of Stanford University. They are the sites of popular creekside trails.
The western slopes of the Santa Cruz Mountains are a different world from the eastern side. Very few roads cross the summit; those that do usually follow old Indian trails or Spanish routes or are remnants of former logging roads. Originally thickly forested, the canyons and ridges now support a second or third growth of redwoods and Douglas firs, interspersed with live oak, black oak, tan oak, bay laurel, and smaller shrubs and trees. Some groves of giant redwoods were spared the axe and saw. Toward the Coastside some areas formerly ranched are still open grassland.
Westflowing creeks are generally larger and longer than Bayside streams, due to the heavier rainfall on the Coastside and the greater distance from the mountains to the sea. Present-day trails follow major creeks flowing through state and county parks to the ocean along routes trod by early settlers.
Geology
The Santa Cruz Mountains were formed over the millennia by the uplifting, folding, and faulting of rocks. Frequent earthquakes in the area tell us that forces deep within the earth continue to reshape the land. The San Andreas Fault, which spans the length of California, is the most influential feature of the Peninsula landscape. It runs northwest-southeast roughly parallel to the main and highest ridge of the Santa Cruz Mountains, popularly known as The Skyline.
In the 1890s Andrew Lawson, a noted California geologist, recognized the rift valley running south toward Loma Prieta and Mt. Umunhum and north up the Crystal Springs Valley as far as San Andreas Lake, about 25 miles in each direction. He named the fault for the northernmost of the rift-valley lakes. The great earthquake of 1906, centered a few miles offshore and west of San Francisco’s Lake Merced, made the San Andreas Fault famous around the world. A dramatic vantage point from which to view this fault is the top of Los Trancos Open Space Preserve on a fault saddle between the Skyline ridge and Monte Bello Ridge.
Hikers mind their footing on the trail to San Bruno Mountain’s summit.
The Santa Cruz Mountains are very young geologically. The oldest exposed rocks on the Peninsula were formed only 150 million years ago, whereas the oldest known rocks on earth are four billion years old. In spite of its youth, Peninsula geology is extremely complex because the area lies at the boundary between the Pacific and the North American plates. These plates have been (and still are) moving very slowly past each other for the last several million years at an average rate of 1 to 2 inches per year. As a result of movements along the fault, granitic rocks originally formed about 90 million years ago in the area now occupied by Southern California lie deep under most of the land west of the San Andreas fault, and are exposed on Montara Mountain.
From the concept of plate tectonics, and the kind of bedrock formation found in the Santa Cruz Mountains, the following geologic history can be inferred. Between 150 and 65 million years ago, massive quantities of lava flows, red ooze, sand, and mud accumulated in complex layers on the Pacific Plate in a location west of what is now the California coast. These deposits on the ocean floor were hardened to rock, partly crushed and thoroughly mixed as the edge of the Pacific Plate was pushed under the North American continent, thus moving what is called the Franciscan Complex to its present location on the east side of the Pilarcitos and San Andreas faults. This complex is composed of shale, siltstone, limestone, sandstone, chert, and greenstone. Outcrops of these rocks occur on Sweeney and Sawyer ridges, San Bruno Mountain, Belmont Hill, and Monte Bello Ridge.
Serpentine, the California state rock, occurs in outcrops along Sawyer Camp Trail, in road cuts along I–280 from Woodside north, in Edgewood Park, and in scattered locations on Monte Bello Ridge. The linear fault valleys of the Peninsula exist because rock broken by fault movements erodes more rapidly than rock farther from the fault. You can see other and more recent signs of faulting on the Peninsula. Where the fault crosses the ridge at the top of Los Trancos Open Space Preserve, the crushed rock has eroded to form a fault saddle. Sag ponds at the preserve result from horizontal fault displacements that shifted hill slopes, blocked ravines, and created undrained depressions. Earthquake movements have changed stream courses along upper Stevens Creek Canyon. Landslides occur frequently in the steep Santa Cruz Mountains; many were triggered by the 1906 and 1989 quakes and their prehistoric counterparts.
The San Gregorio Fault runs northwest-southeast inland from the coast on the west side of the Santa Cruz Mountains. Its effects are seen in the shifts of creek directions near Butano State Park, at Fitzgerald Marine Reserve, and near Mussel Rock.
Plant and Animal Life
In this guide we mention some of the trees, flowers and creatures you may encounter, but we can touch only briefly on a few of the many species. Following are brief descriptions of the major plant communities. Fortunately for those whose curiosity is aroused, there are many excellent publications that focus on the plants and wildlife of the Bay Area and California. See Appendix II.
More than 1700 species grow in the Santa Cruz Mountains and on their western and eastern flanks, categorized into what are known as plant communities—a group of plants with similar tolerances and similar adaptations to environmental conditions.
On the east side of the Skyline ridge there are four main plant communities:
1. Mixed woodlands—characterized by the rounded forms of the oaks, madrones, bays, and buckeyes that cover much of our hillsides.
2. Open, rolling grasslands—a noticeably different community of mountainside meadows and foothill pasturelands. Mostly imported annual grasses, they are green in winter, dry and golden in summer, and characteristic of California and other Mediterranean climates, distinguished by winter rains and summer drought.
3. Conifer forests of firs and redwoods—tall, evergreen trees that cover thousands of acres in the Skyline ridge watersheds, parks, and sheltered canyons. Although the redwoods were cut over in the 19th century, extensive stands have grown again.
4. Chaparral—a dense growth of shrubs and trees specially adapted to winter rains and long, dry summers that thrive on hot dry slopes. Their leathery or waxy evergreen leaves, sometimes curled inward, conserve moisture, and their long taproots reach water deep below the surface. These plants form a scratchy thicket, unfriendly to the hiker but home to many species of wildlife. The Spaniards are said to have named the vegetation “chaparral” after a Spanish evergreen oak, the chaparro.
Coastal Trail south of Miramontes Point
On the west