There were many Nettles growing under a Coast Live Oak, next to the parking lot. I did a "touch test" as @vreinkymov suggested, and skin contact did cause a temporary rash on my hand which hurt for a while. Holding multiple Nettle leaves with my fingers didn't cause a reaction. It was difficult to capture, but I included photo 11 anyway.
I think it's probably Urtica urens, but I'm not great with identifying Nettles and I'm not sure about Hesperocnide tenella.
Photos 1-3 and 4 were edited to have a Flash White Balance in Photoshop. Photos 5-10 were edited to have a Custom White Balance.
Hagador Canyon and Skinsuit Trail, Corona, Cleveland National Forest, Riverside County, California
Hagador Canyon and Skinsuit Trail, Corona, Cleveland National Forest, Riverside County, California
Hagador Canyon and Skinsuit Trail, Corona, Cleveland National Forest, Riverside County, California
Hagador Canyon and Skinsuit Trail, Corona, Cleveland National Forest, Riverside County, California