Yucca plant found near the Upper Winter Creek Trail at Chantry Flats in the Angeles National Forest.
bad photo but the Yucca plant is there high up near Mt. Wilson
In the San Gabriel Mountains of southern California, Mount Baldy "ski hut" trail, elevation probably between 7 and 8 thousand feet.
Charlie pointed out that this could be subspecies parishii. Indeed I'd never seen yucca blooms so robust and with such large stalks. I'll have to take a closer look at the ones in the Santa Monica Mountains next time.