There's a mini market about 3 miles from 1000 trails when you go towards Tres Pinos\Hollister. Can't miss it, first buildings once you turn onto the main rd
There is a motorcycle shop located in Holloister Hills OHV. It's about 8 miles on Cienega Rd. just past a couple wineries. They sell water.
The place is pretty desolate. So you are probably better going to town to get your water
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