Land snails are pretty common world wide, their distribution doesn't really depend on there being fresh or salt water nearby. The shell and the mucous they secrete help them conserve their moisture - because of this they can live even in deserts where you wouldn't expect to see slugs (which are basically snails without shells). One interesting thing is in some desert areas they actually estevate - estevation is basically the same thing as hibernation, but the period of dormant inactivity happens during the summer instead of winter. You should have very similar snails on the mountainsides and forests in Colorado, a generic name for this type of snail is "Rocky Mountainsnail". The land snails we had in Oregon were larger and a dark reddish brown.