Snakes normally stay away from human habitations. The more human presence the less snakes. Yes, you could run across one on a seldom used trail. They try to avoid human contact and if sure of the opportunity they will slither away from you. If feeling trapped they will confront you. The biggest chance of encounters is during or immediately after severe weather when they may have been driven out of their normally secure habitat. Continental US poisonous snakes are rattlesnakes, copperheads, water moccasins and coral snakes.