Likely seeded.
Species inventory of the south branch of Tahquitz Creek where it is crossed by the PCT, done by Tom Chester and Patrick Drew, after about ten minutes of rain and hail. The next-to-last pix shows the surveyed area north of the crossing; the last pix shows the surveyed area south of the crossing from a different vantage point.
Just these three plants seen, but there could have been a lot more hiding amidst dense stands of other plants.