OAKLAND, Cali.—Deep in a redwood forest in California’s Castro Valley, the crowd of about 75 people was hard to miss. Not only because of the DJs kicking off dance parties, tables full of snacks and sparkling water, and people sharing shrooms and cannabis. But everyone there was also “melanated,” as one member described. Some even wore traditional African garments or golden halo crowns.
They’d traveled to the confluence of canyons about half an hour’s drive from downtown Oakland...