This is a banana slug. Like mushrooms, they are everywhere when you go hiking this time of year. I tried to include some clover in the picture for scale. These guys are a solid 4-6 inches long and I didn't adjust the color on this image at all -- that is their god-given color, in all of it's neon yellow glory. A word of warning, do NOT accidentally step on a banana slug while you are hiking. It will take you the rest of the hike to rid your shoe of the even-more-neon-yellow-and-disgusting goo that resides inside the slug. Ick.