Left leg calf muscle at the very bottom of the muscle is very, very rock hard. rest of the muscle is fine. i have no pain or problem when walking?

Hard Calf: Sounds like scarring perhaps you have injured your calf or tendons connecting your calf to your heel, at some point. A partially torn tendon can result in improper healing if left untreated or treated improperly. If no pain occurs with walking or running that's good sign. However, i would recommend stretching daily and self massage to see if it improves and prevent problems down the line.