Wilson Arch is located right 24 miles south of Moab, Utah right next to Hwy 191. It is 91 feet wide and 46 feet high. You can literally see it while driving by, but pull off the road and take a closer look. The arch faces the west, so is best seen in the afternoon when the sun shines on it directly (my picture here is a morning shot). A short hike will take you up to it if you want to walk under it.
To see a list of all the arches and natural bridges I have seen, along with helpful descriptions and directions, go here.