The cleary reserve is located in Pope Valley Township, Napa County, about 16 miles (26 km) northeast of the city of St. Helena.  The Reserve encompasses 430 acres (174 ha) of rugged wilderness at elevations of 1,000 to 2,000 feet (300 - 600 m) above sea level in the Palisades Mountains of Northern California’s inner coast range.  Vegetation is primarily mixed broadleaf-coniferous forest and chaparral within three watersheds, the largest of which is Swartz Creek.


The coast Ranges north of San Francisco Bay are small, linear, and irregular mountains separated by lowlands, which are strings of basins rather than continuous valleys and are typically narrow, but may have broad alluvial plains.  The mountains trend north-northwest to northwest with rounded peeks and steep slopes, and range in elevation from 100m – 1900m.

The principal geomorphic processes affecting the contemporary landscape are mass wasting by flow and sliding, and fluvial erosion.  Runoff is rapid and all but the larger streams are dry by the end of the summer.  Natural lakes are absent, but there are a few reservoirs in the area and stock ponds.


The Cleary Reserve is situated in the Ultrabasic Complex Subsection of the Northern California Coast Ranges Ecological Section.  The subsection is composed of a complex pattern of Mesozoic sedimentary, metasedimentary, and metavolcanic rocks.  It contains Jurassic and Cretaceous Franciscan rocks of the Central and Eastern Belts, including much ultramafic rock, and Cretaceous sedimentary rocks of the great Valley Sequence.


Most of Napa County is dominated by sandstone and shale, which differ greatly in age and weathering and are responsible for differences in landscape and soils.  The northern and eastern parts of the Napa Valley are composed of the Pilocene volcanics.  The soils formed in weathered material from rhyolite and rhyolitic tuff are in the Forward and Kidd series, and have a high content of ash and other pyroclastic materials.


Climate within the Pope Valley is temperate and humid.  It is influence somewhat by marine air but lacks summer fog.


Napa County, in general, is protected from the hot summers of the Central Valley by the coastal mountain ranges and the Pacific Ocean, which is a source of cool, moist marine air that moderates temperatures.  Based on a 29-year period of record from the Pacific Union College weather station, the average annual temperature is 57.01 F.  The highest average temperature of 70.66 F occurs in July as does the maximum average temperature of 86.3 F.  In general, summer temperatures average greater than 60 F between June and October.  Winters are generally mild but there are occasional cold spells.


The average annual precipitation at Angwin is 41.30 inches, of which almost 60 percent occurs between December and February.  Over 92 percent of precipitation occurs as rainfall, with only 3.1 inches of snow annually.  The highest year of record was 1983 with over 88.89 inches.


Cleary Reserve is situated in the inner North Coast Range District of the Northwestern California Floristic Province.  The district extends from southwestern Shasta County along the east slope of the Inner Coast Range to western Solano County near the Sacramento-San Joaquin Delta.  Because of the hot, dry summers and relatively low rainfall, chaparral and pine/oak woodland are dominant vegetation communities.

The reserve has over 160 species of plants, representing 53 families.  The Reserve includes eight species of oak (valley, blue, coast live, interior live, canyon, black, scrub, and tanbark) and five conifer species (foothill pine, ponderosa pine, knobcone pine, MacNab cypress, and Douglas fir).  The small stands of coastal redwood on the Reserve, along Swartz Creek, and Aetna Springs represent the easternmost occurrences of the species in central California.

Although much of the reserve is characterized by an intermixing of plant communities, certain assemblages of plants, including both floristic and structural aspect, are fairly distinct.  These include the Foothill Woodland, Mixed Evergreen Forest, Northern Mixed Chaparral, White Alder Riparian Forest, ponds, and orchards.