You mention bike riding alleviated the pain, and riding hard pack inflamed it, both reasonable indicators of shin splints.
You need to stretch your calve muscles and strengthen your shin muscles. Calves don’t get much work in high boots, but shins bare a tremendous strain splitboarding.
I presume you are familiar with calve stretches, but look up wall push-ups for strengthening the front of the lower leg. A micro fracture is also possible, but I doubt it if the pain subsided after the season.
There is a wealth of info on running web sites if you Google shin splints and also compartment syndrome (nasty problem, I know from experience) both share similar exercises for strengthening and stretching the muscles.

I had a brutal shin splint problem for running (but never for splitting). I had to take a bit of a break and slow things down. What solved it for me was tying a bike inner tube (I used a big fat DH one) to the leg of my couch, lying on my back (feet towards the couch), and stretching out the tube with my toes as much as many times as I could stand two or three times a day. It sorted me out surprisingly fast – like a week or two. There is lots of info here: http://www.ultrunr.com/shins.html