ENVIRONMENTAL SETTING

The natural heritage of Hollister Ranch includes a rich flora and an interesting series of vegetation types that reflect the contrasting geologic substrates, Mediterranean climate, maritime influences, and location in a biogeographic transition zone between northern (or central) and southern California. The wide variety of habitats support a surprising number of the major plant community types represented in Santa Barbara County. The flora includes species that reach their southern or northern limits of distribution in this area as well as regional endemics, which contribute to the uniqueness of the natural resources at the Ranch.

Climate. Hollister Ranch is characterized by a Mediterranean climate with mild, moist winters and moderately warm, rainless summers (Fletcher 1983). Point Conception, a few miles to the west has been treated as a major climatic boundary (Barbour et al. 1975), with relatively cool and moist conditions to the north and warmer, drier conditions to the east and south.

The climate of Hollister Ranch is affected directly by the prevailing westerly transoceanic air currents. These currents often produce stronger winds on the west-facing coast north of Point Conception and in the adjacent east-west trending Santa Ynez Valley than at Hollister Ranch, which is situated mostly along the south-facing coast east of Point Conception (Fletcher 1983). When moderate to strong winds occur, they spill over the crest of the Santa Ynez Mountains in the vicinity of Hollister Ranch. Higher wind velocities occur on the northern margin of the Ranch and mountains, where wind-pruned trees and shrubs are common at exposed sites.

The regional coastline also is characterized by an atmospheric inversion layer that traps cool moist air at low temperatures, which often contains moisture that condenses as fog in the morning hours. The fog is heaviest and most frequent in the late spring and summer, corresponding with warming of interior lands, when morning air comes into contact with cool ocean water and then is drawn over the land. These mild coastal conditions provide an ameliorating influence at Hollister Ranch for what would otherwise be a warmer and drier environmental setting. The average temperature is 59' F (15' C), with an average daily high of 70' F (21' C) and an average daily low of 47' F (8' C) (Fletcher 1983). Precipitation occurs primarily between November and April, with recorded amounts of rainfall between 6" (15 cm) and 21" (53 cm) for Point Arguello to the west, and between 10" (25 cm) and 24" (61 cm) for Salsipuedes gauging station to the north (Fletcher 1983).

Primary factors affecting the Hollister Ranch environment are the frequent strong winds particularly in the spring, the consistently mild temperature that rarely dips below freezing, and the variable and generally light winter rainfall. The warm air and proximity of the Ranch to a relatively cold ocean creates morning coastal overcast (Fletcher 1983). However, ocean temperatures are much colder north of Point Conception than to the south due to a south-flowing current, which causes a counter-clockwise eddy in the Santa Barbara Channel resulting usually in warmer water along the Hollister Ranch coast than to the north.

The amount and timing of rain, minimum and maximum temperatures, and wind determine, in a broad sense, the plant species that occur in a region such as the south- central coast of California. Locally, the influences of weather are moderated by topography that provide microcilmatic conditions, such as a sheltered ravine that offers protection from drying wind, a sunny south-facing slope that warms up early in the year, or a shady north- facing slope that retains moisture throughout the dry summer. The effects of microclimates can be influenced by geology in another way, through the soils that are characteristic of different geologic formations (Figs. 4 & 5). For example, sandy soils are porous and hold little water, exacerbating drought. Clay soils dry out slowly, and may form an impervious layer that causes water to pond on the surface.

One of the most important biogeographic boundaries in California is the distinction between northern and southern California. This division occurs on the coast in the vicinity of Point Conception, where the western extent of the east-west trending Santa Ynez Mountains block ("cut off") the cold northerly storms. Plant species south of this ridge tend to be more drought-adapted than many of their northern California counterparts. Many northern coastal species or subspecies reach their southern range limits in this area, and likewise, many southern species have their northern limits here. Hollister Ranch is situated in this transition zone, and its flora contains both northern and southern elements.

Geomorphology and Structural Geology. Hollister Ranch is located south of the South Coast Ranges and the Santa Maria Basin in the westernmost portion of the Transverse Ranges Province. The Ranch occurs on an east-west trending homocline, which is made up of marine sediments that dip 40-60 degrees. This homocline and the anticline that it becomes to the east form a portion of the Transverse Ranges known as the Santa Ynez Mountains. A major fault, the southern limb of the Santa Ynez Fault, strikes southwest through the eastern portion of the ranch, transversing Agua Callente and Alegria canyons and trending seaward to the southwest at Alegria Point. This fault has a lateral displacement of ca. 0.5 miles (0.8 km), with the south block moving relatively to the cast.

The topography reflects the south-dipping marine sedimentary rock formations approximately 15,000 feet thick and of varying composition and resistance to erosion, forming a series of subparallel ridges and valleys (Fig. 3). The most prominent landscape feature of Hollister Ranch is the pattern formed by these cast-west trending, uptilted sedimentary rock formations. The erosion resistant Monterey Shale and Vaqueros Sandstone appear as high points in the foothills, whereas the Rincon Formation appears as slumping clay slopes. Matilija Sandstone forms the ridge crest. Stream flows cut through the various formations down to the sea, so that it is possible to walk along a canyon through a geological transect from the youngest formations at sea level (e.g., the Sisquoc Formation and Marine Terrace Deposits) to older rocks (e.g., the Matilija Sandstone and the Santa Anita Shale) at the top of the ridge.

Geological formations have a strong influence on vegetation, as can be seen from a comparison of the vegetation and geology maps (Figs. 4 and 6). Soils derived from the different types of bedrock support dramatically contrasting bands of vegetation. For example, grasslands and coastal scrub cover the deep clay soils of the Rincon Formation and the coastal terraces that overlie the Sisquoc Formation. In contrast, dense chaparral occurs on the slopes of the rocky, fractured Alegria and Matilija formations. The boundaries between types of vegetation are often abruptly-defined, along an east-west trending axis, by the rock formations that underlie them.

The canyons of Hollister Ranch extend up to three miles in length, trend north-south, and form a series of drainages that support forested riparian corridors (see section 111, Fig. 6). Some have perennial flows that often arise from springs, including some that are sulfur-affected, along faults that intersect the canyons. Various wetland types occur in association with the perennial and intermittent flows. A few of these drainages (e.g., Santa Anita, Alegria, and Agua Caliente canyons) support small estuaries when they reach the coast (Fig. 6). Vertical bluffs rise 50 to 100 ft above the beach along much of the coastline. There are a few coastal sites sufficiently protected from wave action that low, narrow dunes can form. At the top of the bluffs, a marine terrace forms a coastal plain, which becomes up to one-half mile wide at the broader, western portion of the Ranch.

Bed Rock and Soil Types. Fletcher (1983) reviewed the major geologic formations that crop out at Hollister Ranch and their corresponding soils. This discussion (also see Norris and Webb 1976, Dibblee 1988, Thompson and Prothero 1998, Ehrenspeck 1998, and Fig. 4) is in order of youngest to oldest formations from the coast to the northerly property line. Refer to section 111, Land Use History, for a discussion of changes in post- glacial shorelines relative to Chumash use of intertidal resources.

The rock formations that occur at Hollister Ranch represent sediments that were deposited largely in marine environments. As a result of the relative movements of the Pacific and North American plates of the Earth's crust, these rocks have been folded and faulted into their present configuration. Atmospheric, decomposition, and fluvial processes such as erosion and deposition have produced canyons, valleys, terraces, and ridges, and have resulted in the formation of various soil types.

The Sisquoc Formation is a gray, diatomaceous shale or claystone that is Pliocene in age. It contains fossilized whale bones and is estimated to be 12-6 million years old (myo). It underlies much of the coastal plain and crops out at sites such as Bulito, Drakes, and Sacate beaches. This formation was cut by wave action into a Pleistocene marine shelf, following which it was overlain by a layer of clay and then uplifted above wave action. These Marine Terrace Deposits and the underlying shales form the dominant soil types including the Agueda silty clay loam, Botella silty clay loam, Concepcion sandy loam, and Diablo clay (Fig. 5).

The Sisquoc Formation lies conformably (without an erosional surface) on the Monterey Formation, which is a light buff to pale brown, silaceous shale interbedded with softer shale and limestone that is Miocene in age, ca. 20-15 myo. The Monterey Formation was deposited in deep ocean conditions and composed largely of diatoms. It forms the first steep rise north of the coast, and crops out at visible sites near the mouths of Agua Caliente and Alegria canyons (Fig. 4). The soil layers associated with the Monterey Formation are thin or nonexistent. The Lopez-Rock outcrop complex and Santa Lucia shaly clay loam are named examples (Fig. 5).

The Rincon Formation is a gray, weakly consolidated, clay-shale that lies unconformably (with an erosional surface) under the Monterey formation. It also was deposited in a deep ocean environment and is Miocene in age, ca. 20-15 myo. The Rincon Formation is approximately 1500 feet thick and occurs in all canyons at Hollister Ranch (Fig. 4). It weathers to soil of the Nacimiento Complex (Fig. 5), which is a black sticky adobe soil that is characterized by slumping and sliding. It forms the east-west trending topographic lows immediately north of the Monterey Formation, and is characterized by grassland vegetation (Fig. 6).

The Vaqueros Formation lies below the Rincon Formation and is a Miocene (ca. 25-20 myo) sandstone matrix that is approximately 400 feet thick and resistant to weathering and erosion. It is fossiliferous (e.g., pectens, oysters, and snails) and contains green-brown pebbles and rock fragments. The formation crops out as a narrow band forming the first open rock faces (in the form of a rock wall) northward up canyons from the coast (Fig. 4). There is an abrupt topographic expression of the contact between the shales and grasslands of the Rincon Formation and the sandstones and chaparral of the Vaqueros Formation (Figs. 4 & 6). The exposedsubstrate is classified as the Gaviota-Rock outcrop (Fig. 5).

The Sespe Formation is a maroon, brown, tan, and green set of strata deposited as onshore river sediments that have formed sandstone and siltstone-shale. It is Oligocene to Eocene in age (ca. 30-25 myo) and is approximately 1200 feet thick east of the Ranch, but thins to very little at Agua Caliente, or none to the west (A. J. Field, pers. comm. 1998). The Sespe Formation is not very resistant to weathering and erosion, and thus forms saddles between parallel ridges of resistant sandstones where is does crop out. The Aleglia Formation is Eocene in age (ca. 34-30 myo) and is composed of red to buff sandstones and shales approximately 600 feet thick. It contains shell fossils including oyster beds, and is thought to be the marine equivalent of the non-marine Sespe Formation (Thompson and Prothero 1998). The Alegria is expressed mostly as Los Osos Maymen clay and Los Osos clay loam at Hollister Ranch (Fig. 5).

The Gaviota, Sacate, Cozy Dell, and Matilija formations (Fig. 4) are Eocene in age (ca. 55-35 myo) and form the "core" of the Hollister Ranch and the crest of the western Santa Ynez Mountains. The Gaviota Formation is composed of massive siltstone exposed as buff-colored rocks north of the Vaqueros Formation. A thick sequence occurs in the Cojo and Alegria canyons, but is thin at other sites. Gaviota sandy loam is the soil type (Fig. 5). The Matilija Formation is a thick-bedded buff-colored sandstone found along the crest of the Ranch and the Santa Ynez Mountains, west of Santa Anita Canyon. It can be identified by the presence of mica sparkling from the sandstone (A. J. Field, pers. comm. 1998). The most impressive outcrops occur above San Augustin and Cementerio canyons. The substrate is mapped as the Maymen-rock outcrop complex (Fig. 5). The Anita Formation is the oldest Eocene formation exposed on the Ranch, and is a massive foraminiferal claystone that has limited exposure on the north side of Long Canyon near the head of Bulito Canyon. Maymen stony fine sandy loam and Los Osos clay loam (Fig. 5) are associated with the Anita Formation. The Jalama Formation, which is late Cretaceous in age (> 65 myo), contains the oldest rocks in the area, and is characterized predominantly by Maymen stony fine sandy loam along the north-central boundary of the Ranch (Fig. 5).

The diverse and contrasting topographic, geologic, and soil features of Hollister Ranch contribute to the many special habitats for plants, and thus are important in determining the diversity of the botanical resources that make much of the Ranch a biologically rich and important natural area. The location of Hollister Ranch within a major transition between northern and southern biogeographic areas, and the ameliorating affects of its proximity to the Santa Barbara Channel, contribute to the enrichment of the Ranch's biota and the presence of many plant species of special interest.