This is a Pacific or Western plum (Prunus subcordata, Bentham) and it is a native species found growing wild in a relatively limited region east of the Coast Range from southern Oregon to central California. It occurs in greatest abundance in Lake and Klamath counties in Oregon and Modoc and Sierra counties in California. While the greatest concentration of the native thickets in California seems to be in the general vicinity of Mount Shasta, the plum is found in more or less abundance east and south of the Nevada line, especially in the foothills of the Sierra Nevadas. It has been reported as far south as Yosemite Valley. The plum usually forms thickets of small to large shrubby trees along streams in canyons, on hillsides, or in the open area of pine forest. In other cases the thickets are found on ridges which are thought to be the shore lines of prehistoric lakes. There is a general similarity in the sites on which the plum thrives and spread throughout the region, so much so that one can almost predict the location of the thickets. The largest trees are found in these thickets growing on the deeper, sandy-loam soils in the canyons where water is ample, and the richer bottomlands adjoining the old lake beds. The hardiness of the species and its ability to adapt itself to adverse conditions is typified by the scrubby little thickets found growing out of rock slides at high elevations. An occasional thicket is found, however, where drought or exposure has all but killed out the stand. The region in which the plum is native has an elevation of 1,000 to 5,000 feet, although it has been observed growing in favorable locations in the mountains of the region at elevations as high as 6,000 feet. At these higher elevations the plums are less apt to bear crops and are late in ripening.

Thanks, anitamo. It took a lot of googling to find a picture of the seed pod - my pic - but you got it. Latin name's Microseris linearifolia, and there's a picture of both the flower and the seedpod here: http://wc.pima.edu/Bfiero/tucsonecology/plants/wflow_sipu.htm There are a lot of varieties, though and I wouldn't venture to guess which one it is. I saw it where the San Joaquin valley meets the Tehachipis and not far fom the Sierra Nevada foothills, so it could be any one. Here's the Wikipedia page: http://en.wikipedia.org/wiki/Microseris EdB

I don't know what it is, but i cut one down on my property. It grew from seed and within two years, it was about 25 feet tall! I have seen them planted in parking lots here and also growing wild (not sure if native or introduced) in the foothills of the Sierra Nevada (Millerton Lake to be more specific).

Al, These plants were uprooted and subsequently planted, as I mentioned in the original post. I had to put them in soil as soon as possible and I doubt anyone, even an experienced gardener like yourself, could have avoided the stress of transplant unless they dug out a block of dirt when moving them. These were growing in a gravel driveway and were going to be sprayed with herbicide. I saw the opportunity to save a few. That is all. I find your comment very condescending.