[13] The creek bed is fairly steep in the upper reaches and through the canyons, flattening out in the plains that open to Big Valley.

[8] The region holds greywacke sandstone, chert and serpentinite rocks of the Franciscan Assemblage that have been highly sheared and faulted with ridges and valleys trending northwest–southeast.

It is a narrow corridor that runs northwest through the Northern California Coast Ranges into Big Valley, a flat region south of the western part of Clear Lake.

[16] The Geysers geothermal field includes the upper Kelsey Creek Watershed, as well as parts of Lake and Sonoma counties to the south.

[17] A 1981 report noted that geothermal plants in the Kelsey Creek area were causing air quality problems through hydrogen sulfide emissions.

Construction of roads and drill pads opens large areas of soil to erosion by heavy rains, washing into the creek's tributaries and degrading water quality.

[18] Annual precipitation in the upper part ranges from 25 to 80 inches (640 to 2,030 mm), with highest rainfall along the crest of the Mayacamas Mountains.

[11] Better roads in the early 20th century led to an increase in production of walnuts, pears and grapes, mainly in the flat part of Big Valley.

South of Big Valley in the higher country, the main vegetation is blue oak woodlands, gray pines and annual grasslands.

Above about 2,000 feet (610 m) the main land cover is chaparral, with patches of California live oak woodlands on the higher ridges.

Invasive and introduced species such as catfish, bass and carp into Clear Lake, as well as historically low creek water levels and diversions are also believed to have contributed to the hitch's population decline.

[22] The rainbow trout (Oncorhynchus mykiss), native to Clear Lake, seems to have been introduced in the upper section of Kelsey Creek after the arrival of white settlers, and several fisheries developed in the area.

[17] In the early 1920s, Jim McCauley established a resort on the creek between Cobb and Whispering Pines, west of his Boggs Mountain property.