When walking on the treadmill or hiking for longer than 45 minutes, I get numbness on the bottom of one foot.  it feels like its asleep. What is this?

May not be so simple. Exercise related foot numbness can be a presenting symptom of sciatica, although more commonly would also be expected to be painful. Another possibility is peripheral vascular disease, meaning decreased blood supply to the lower leg. If you have weakness in your foot, your leg gives way or have any wounds on your foot you did not feel, consult your physician soon.
Shoe inserts. It sounds like your feet are not being adequately supported. Get some insoles for your shoes and see if that helps. If not, then see your doctor or podiatrist.