Not too far off I-70 is this small arch. It takes a little effort and travel on dirt roads to get to. In the same area - the "Head of Sinbad" are the broken off pictographs as well. This is an area of the San Rafael Swell which has other fun things for those discerning enough to search.
Take a 5 mile good dirt road just outside of town to the edge of the Green River and you will come to the site of a human made cold water geyser. I haven't seen it go off, though I hear it is great, especially on a hot day. It isn't like Old Faithful, no regular eruptions and no one around to tell you when the last one happened, so you either get lucky or bring food and water and spend the day/night.
(ps thanks to vtveen who introduced me to it.)