Aliases: Bigelow Thistle, Cobwebby Thistle
If your expedition is seeking California Thistle, you can leave the magnifying glasses and macro lenses at home. The many-flowered heads are big (yes, that's a full-sized bumblebee in the above photo) and the plants are usually 2 - 4 feet tall. It's at home on dry hillsides, common along Highway 140 in the Merced River Canyon and along the Hite Cove trail, and I've also seen it growing in various spots along Highway 41 in southern Yosemite.
Blooms: April - July
Cirsium occidentale etymology: Cirsium derives from the Greek word for thistle, and occidentale from the Latin word meaning "western," or more accurately, "of the western sky." Californicum is anybody's guess; perhaps someday some intrepid researcher will get to the bottom of it.
This Photo: Along the Hite Cove trail, early May