It's one of the armyworms, might even be the Beet Armyworm. If you google that one, you'll see a jillion differing images as they vary soooooo much from the time they hatch until they are mature.

Just FYI, next time you see a caterpillar, you can usually find what it is by knowing what plant it's on. For example, if you google "beet host plant" you'll see lots of entries for beet armyworm. Once you get an idea, you can look at pics to confirm. Caterpillars usually have a single plant or just a few plants that they can eat.