I fracture my L1, am i allowed in the Marines?

Drew, if you were cleared for physical activities that means you can do work. The thing that you should have done or still do is talk to the orthopedist that saw you. Ask if the fracture is solid enough for the amount of stress that it is going to undergo in basic training. If that answer is yes then you are good to go. Remember that unless the induction includes an x-ray they are not going to know unless that area gets injured. Just make sure that your hip extensors, hamstrings, and back muscles are strong enough to handle the workouts you are going to face.