If you're starting your trip in Las Vegas, it generally makes sense to see both Zion National Park and Bryce Canyon in one day.  From Las Vegas you'll head up Interstate 15, through the Arizona Strip and the Virgin River Gorge, before making for Zion.

You'll have a chance to view the Visitor Center, before driving through Zion and seeing the incredible display of towering cliffs and rock formations.  The trip will take you through the lower elevations of the park, before climbing the switchback road up through a tunnel that has been blasted into the sandstone.  As the vehicle climbs up the road, the cliffs fall off to the one side, and tower up to the skies on the other.  The vegetation is diverse, interesting, and, often colorful.

It's only about a 100 minute drive from the east entrance of Zion to Bryce Canyon, along one of Utah's most picturesque backroads.  After exploring Bryce, the quickest way back to Las Vegas, is to re-trace our steps, and so you get to go through Zion one more time, this time dropping down the switchback, to the bottom.

A tour of Zion National Park generally starts in Las Vegas, but can also begin in St. George, Cedar City or Salt Lake City.