I took the mountain bike out for ride this weekend. It was a muddy adventure.
A couple of years ago, I slapped some fenders on my GT for commuting duty. It was perfect for rainy or snowy rides back and forth to my office in Cambridge. When I lived on Nantucket, the sandy roads and occasional trail posed no problem. There generally wasn't much mud.
The pics below are why you should remove fenders for trail riding in Colorado. The mud was packed in so badly that the wheels wouldn't turn. I had to remove the wheels and clean out the thick, sticky mud several times on my ride yesterday.