A Cardon cactus, with Phil standing to the right of it. These things get really big (up to 70' tall), and we saw one about 50% bigger than this but it was off the road where there was no place to stop.
Unlike roads in the USA, the roads in Baja end at the edge of the pavement, where there is often a 12" (or more) drop to the side of the road -- very hazardous to try to pull off the road.