I'll get booed by some, I'm sure, but I say hats off to the sheriff's department. I love to ride, including off road at some points in my life. I'm also an old-fashioned conservationist at heart, as well as having enjoyed many trails in the San Juans and other parts of Colorado over the decades. It dismays me to see trails - even posted wilderness area trails - that have been turned into 5' tracks of loose dirt by motorized vehicles.
Once on a trail north of Crested Butte, I had to get off the path - in a restricted, posted, fenced wilderness area - because of A Geo Tracker who had found his way in and was driving up the trail. Another time, I hiked up to the ghost town of Holy Cross City in the Gunnison NF, and found that the beautiful but fragile meadow had been torn up by people doing donuts. The track up is a sanctioned Jeep road, but the meadow was obviously off-limits; it was posted off limits even for walking! I assume the Jeep club that takes responsibility for maintaining the track didn't do it.
As Derek points out, there are plenty of legal, posted roads and trails crisscrossing the San Juans. No need to ruin the fragile foot trails or treat wilderness hikers to the sound of 4-cycle engines.