Jeffrey S.
Yelp
NOTE: This petroglyph wall is not located in Monticello, but outside of town about 30 minutes. It's on Highway 211, on your way from US-191 into the Needles District of Canyonlands. I fixed the pin drop marker here on Yelp, but these things can be finicky. It's marked and on the side of the road, but GPS crowds can set to: 37.9879209, -109.5188924.
Man, I really love this spot. I mean, it's a nice little get-out-and-stretch and won't take you more than a few minutes, but it's a nice roadside pull-off when you're already off and rolling on adventure. I first visited in 2005 or so and was struck by just how prolific all the petroglyphs are. Sometimes you only see a few in one place, but here at Newspaper Rock, it's plastered with characters.
Pull off the highway, park, and walk up the paved path. It'll take you less than two minutes, so almost anyone from grandma to the little ones can make it. There's a small fence at the base of the rock to keep you from touching the panel, but you get a front row seat to the artwork.
This is very near a campground, but there is a small toilet facility here so you can hit that up before you get into the park, or out to Lockhart, or wherever your travels are taking you.
Note that this is not the only panel in the area. If you keep driving, pay attention to the cliffs and the walls around you--you can spy a few characters. But they're sparse, and in comparison to this amazing display, they may barely register. That's what makes this mysterious spot (but why were ancient inhabitants all tagging it???) so wonderful.