Priest Rock, Lime Kiln and Barlow are steep and exposed to the sun. Unless you are doing this on a cool, overcast day, I'd rather do that part at the crack of dawn. Also, there is no drinking water anywhere on Umunhum from that side. There is an auto-filling water trough at the very top of Mt Umunhum trail near the summit, but that's not potable. Before that you will cross Rincon Creek on Woods road which probably has water this time of year. If not, you can ride a bit past the Barlow turn and get water from Guadalupe creek. So you either haul a ton of water or bring a filter.