I think much depends on the time of the year. This year at the Ranch we had a cool Spring and went right into very hot Summer. During the Spring I had a large number of snakes but once the heat hit they were gone. As Fall arrives they will be coming back towards the den under my deck(I hope).
I was out herping on Sunday looking for T.s.parietalis(Red Sided Garter snakes) and didn't see a single one. Once again the heat was playing a part in that. I think Spring and Fall in any good garter snake herping area is best.