You can start right at Highway 191, but the first 2.8 miles are easy to drive for passenger cars, and this section of road is not too interesting, so it's better to start from the Klondike Buff parking area, 2.8 miles along this road.
From here, the first section is very popular as it's the main access for all of the Klondike trails. Bikes use a variation that parallels the road to the west and is a little less sandy than the main road, though there are still sections you might have to walk.
Where the Klondike trails start, you'll take a right to continue on a slightly bumpier road until you hit an enormous section of slickrock. You might find dinosaur prints if you're lucky.
Continue until you get to the border of Arches National Park, where a sign lets you know that bikes cannot continue. You can leave your bike at the border and continue by foot a short ways to a great viewpoint of Arches National Park and the La Sal mountains.