Perhaps what is so alarming is their rapid movement -- that uncanny ability to slide and slither and twist... Combined with their camoflage, snakes often aren't spotted until they do move, and they are usually moving fast. It's a startle reflex to jump away, and it serves a useful purpose for the snake as well. Best to just leave them be, out there. If you do need to relocate (as we did with Reginald, because he was frightening guests), pick them up gently. Support the middle of the body, and if necessary, gently lead the head away from a direction you don't want them to go.
Snakes feel quite amazing. They are dry, not slimy, and they heat their bodies by basking in the sun. In winter, the garter snakes gather together into dens, called hibernaculums, and all spend the winter tangled together -- a technique that provides sufficient heat to keep them all comfortable.