Harnach, W. 2016. Annotated checklist of the flora of the Sierra Valley region of Sierra and Plumas counties, California. Phytoneuron 2016-13: 1–121. Published 17 February 2016. ISSN 2153 733X ANNOTATED CHECKLIST OF THE FLORA OF THE SIERRA VALLEY REGION OF SIERRA AND PLUMAS COUNTIES, CALIFORNIA WILLIAM HARNACH P.O Box 28 Calpine, California 96124
[email protected] ABSTRACT The Sierra Valley region of California is unique in that three floristic zones converge in this mountain valley, the Sierra Nevada from the west, the Great Basin from the east, and to a slight degree the Cascade Range from the north. A checklist of the flora includes 93 families, 434 genera, and 1153 documented species; geographic ranges of another 125 species suggest that they also may occur in the area, for a total of 1278 species. Sierra Valley is a large mountain valley located east of the Sierra Nevada crest. The geology of this region is complex but in a simplistic form it is a down-faulted block basin (graben) filled with volcanic ash deposits and lake sediments, similar to Lake Tahoe in geologic origin. This has resulted in an inverted “L” shaped flat basin, with an average elevation of 4900 feet over an area of approximately 208 square miles. The entire checklist area is approximately 360 square miles. Figure 1. The Sierra Valley –– area covered by the checklist. General notes In 2007 I began to compile a list of plants found in the Sierra Valley region for the the 2008 Jepson Herbarium Workshop “The Flora of Sierra Valley,” which my wife and I lead.