This is a cactus
(not a mushroom) which grows wild in Texas
among other places. It is a hallucinogen
when properly prepared that also plays an important part in certain Native American
Oddly enough, it the United States it is legal to harvest and use this plant for religious ceremonies, but not to plant and cultivate it. Unsurprisingly the wild population is dwindling, despite those who feel bound to disobey the law, if only by returing the seeds to the wild.
Carlos Castenada wrote extensively of experiences with peyote, but the scholarly consensus is that he lied.
One of my sources is http://www.entheomedia.com/peyote_crisis.htm.