Spotting

This is a non-venomous gartersnake, which is a very common type of snake across the United States. This one is not being aggressive but rather it's being defensive (yes, there's a difference). We are big and by comparison, they are quite small, so we are considered to be a threat to them when they are exposed and have nowhere to escape to. Garters and many other non-venomous snakes will flatten their heads and puff up their bodies in order to try and look larger. They hope this will frighten the predator and cause it to move on so the snake can get away to a safer place. Hope this helps explain the behavior you were seeing. :-)

poisonous

Northern brown?