Yulupa Creek rises in the Sonoma Mountains, on the southwestern edge of Annadel State Park near Bennett Ridge Road. It descends initially to the southeast. After about 2 miles (3 km) it meets Bennett Valley Road, which it follows eastward to Warm Springs Road, where it discharges into Sonoma Creek.
Watershed
The Yulupa Creek watershed comprises an area of approximately five square miles, and is considered a viable steelhead, Oncorhynchus mykiss, spawninghabitat; stream surveys conducted from 1966 to 1986 indicated significant, but declining populations of anadromous fish.[4] NOAA fisheries has designated the Yulupa Creek watershed as "Critical Habitat" for Oncorhychus mykiss as well as O. tshawytscha (Chinook Salmon) as of 2004.[5]
Close-up of bunch grassunderstory in upper reach of Yulupa Creek within oak woodland.
In addition to known spawning area for O. mykiss, Yulupa Creek has been designated as a high quality riparian zone and an identified habitat of freshwater shrimp.[6] Moreover, the upland watershed area is a California oak woodland, much of which is a relatively undisturbed ecosystem with considerable biodiversity. These forested areas have been characterized as some of the best examples of such woodlands.[7] An unusual characteristic of these forests is the high content of undisturbed prehistoric bunch grass understory, testifying to the absence of historic grazing or other agriculture.
Many of Yulupa Creek's high headwater tributaries are dry in the summer, since rainfall is highly seasonal, with most of the approximately 30 in (76 cm) of annual precipitation occurring between the months of October and April: however, Ledson Marsh retains some smaller pools of water throughout most of the year. Ledson Marsh has a southern outlet to the north fork of Yulupa Creek.
The Yulupa Creek watershed was below the Pacific Ocean floor as recently as the Miocene era, around which time massive uplift and volcanic action formed the massif which comprises the headwaters higher elevations of the watershed of today. Elevations within the drainage basin of Yulupa Creek range from about 430 to 1,800 feet (130 to 550 meters) above sea level. Sandstone is the dominant rock type, as a remnant of the ancient sea floor. Slopes within the headwaters area commonly range from 15 to 30 percent, and lower reaches have gradients of two to five percent. One of the major soil associations within the upper elevation riparian zone is Goulding cobbly clayloam, which contains roughly 25 percent cobblestones, as well as some basaltic exposures, betraying the volcanic past of the Sonoma Mountains formation.[8] Typical soil depths in the headwater area range from 14 to 20 inches (36 to 51 centimeters). Much of the soil type in the Yulupa Creek riparian zone consists of Laniger loam, with rhyolite outcrops, another relic of the igneous history.
Bridges
Looking upstream at Yulupa Creek from the Warm Springs Road bridge
There are two significant public roadwaybridges across Yulupa Creek. The lowermost traverses the creek on Warm Springs Road, 11.15 miles (17.94 km) north of State Route 116; this seven meter span was constructed in the year 1930 with a concrete culvert design using frame culvert construction. A second crossing farther upstream is the traversal of Bennett Valley Road at a point 0.6 miles (0.97 km) west of Warm Springs Road; this year 1970 bridge is of concrete slab construction, with a span of 33 feet (10 meters).[9]
^U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012-03-29 at the Wayback Machine, accessed March 10, 2011
^Santa Rosa Quadrangle, Fifteen minute series, USGS Quadrangle Map, U.S. Government Printing Office, Washington DC (1958)
^Endangered and Threatened Species; Designation of Critical Habitat for Seven Evolutionarily Significant Units of Pacific Salmon (Oncorhynchus tshawytscha) and Steelhead (O. mykiss) in California, United States of America Federal Register: December 10, 2004 (Volume 69, Number 237, pp. 71929-71978
