Many people assume California's Mojave Desert has tall Saguaro Cactus. Those people are wrong. The Mojave Desert does have a wide variety of plant life, though, including Joshua Trees made famous by the band U2 in the '80s. Oddly, while Joshua Trees grow alongside the BNSF mainline through the desert, they don't grow in Cajon Pass. Cajon Pass does have a lot of Chaparral Yuccas (also known as Our Lord's Candle, Spanish Bayonet, Quixote Yucca or Foothill Yucca), a species of flowering plant that, after about five years, grows stalks as tall as 9' to 10' high and covered in hundreds of elliptical (bell-shaped) white to purplish flowers. Following the flowers, the Chaparral Yucca then grows fruit capsules, as seen here, which will split open to spread their seeds upon maturity. After that, the plant dies.
Union Pacific manifest train MOGWC 10 passes a Chaparral Yuccas covered in fruit as it begins its descent down Cajon Pass on its way from Ogden UT to West Colton CA.
(Silverwood, Cajon Pass California - July 13, 2019)