Sticky snakeroot. Formerly called Eupatorium adenophora.
This is an invader from Mexico. The federal government classifies it as a “Noxious Weed”, while the California Invasive Plants Council considers it as having “Moderate” impact in California.
Found on Cold Spring, San Ysidro, Buena Vista and Romero trails at their starts, down in the creek.
There is an umbrel of composite flowers of 5 petaled flowerettes.
Small dandelion-like seeds
This plant was identified for me by Allen Braithwaite. Before that I called it “No Idea 0”.