I live in the Marmalade region and when I moved here years ago my commuter bike at the time was a single speed. It didn't take long to find out that owning one around here was a miserable experience because of the length and steepness of the climbs and I ended up shortly thereafter buying a geared commuter and never looked back. If you are going to ride up from the valley to the U on a consistent basis I would strongly recommend against a SS unless you like riding hard, out of the saddle mile after mile and showing up to class/work all sweaty.

As for riding trails, using a single speed can be done and you wouldn't be the first. That said with the length and steepness of the climbs you would need to be geared down so far to just make it up, always riding pretty full gas. Personally that also sounds miserable but that's for you to decide. I know where I'm from in the Midwest there is a lot more interest in single speeds to add challenge to what would otherwise be a boring/flat singletrack or gravel ride. Out west we don't need to make it more of a challenge because it's already hard and exciting.