The eastern terminus is the East Rim Trailhead, located on UT-9 within eyesight of the East Ranger Station. The western terminus is Lee Pass, located 4 miles up the hill from Exit 40 on I-15.
Time of Year
There are two optimal seasons to do the Zion Traverse. The first is in the Spring (April and May): the high country has just melted out, natural water sources are flowing, and temperatures are reasonable. The other season is the Fall (September-November): temperatures have cooled from their summertime highs and natural water sources are hopefully flowing again after the monsoons. I would not recommend trying the Traverse in the winter (December-March)—when considerable snowpack will slow/halt progress and/or pose considerable risk due to steep snow-covered rock slabs—or in the summer (June-August), when temperatures will be uncomfortably hot and natural water sources may be dry.
Eastbound or Westbound
Since Lee Pass is 400′ higher than the East Rim Trailhead, at first glance it might seem advantageous to go eastbound. However, first-hand experience and the elevation profile and suggest otherwise: eastbounders must gradually and consistently climb for 20 miles, from Mi 4.5 in the La Verkin Creek Valley to Mi ~25.0 at the high point on Horse Pasture Mesa; and they begin their biggest climb (out of the North Fork) late in the route, at Mi 37.9. In contrast, while westbounders climb 400′ more than eastbounders, they do their biggest climb early in the route when they are still fresh and they have a continuous 20-mile stretch of fast run-able downhill. The final climb to Lee Pass can be a struggle for westbounders but it’s short-and-sweet: 1,000 vertical feet over 4.5 miles.
Elite ultra-runners should expect the route to take 8-10 hours depending on their effort. I finished in 9 hrs 27 min after casually running and hiking the first 20 miles. Karl and Jared finished in 10 hrs 24 minutes, which was a “fun” pace for them. I think that a strong “record” time would be under 8 hours. Strong, near-the-front-of-the-pack runners should expect to finish in 10-13 hours. Recreational and casual runners can expect to take 13-17 hours.
Car Shuttle & Parking
This run would be difficult—if not impossible—without multiple groups and/or a designated shuttle/support driver. The basic problem is that the termini are inconveniently far apart: 56 road miles and 80 minutes of drive-time.
If you are fortunate enough to have a shuttle driver, they can drop you off at Lee Pass or the East Rim Trailhead in the morning and pick you up at the other terminus in the evening; if they are really nice they can also crew you with fresh water and food along the way (see the “Key Stats” section for possible access points).
If you have 2+ groups then a “key swap” is the optimal system: it avoids the need for shuttle drivers and/or having to pick up a car post-run. The key swap is easy: Group A drives to Lee Pass, hides the key in a key-determined location, and runs east; Group B drives to East Rim Trailhead, hides the key, and runs west. When Group A arrives at East Rim Trailhead, they find the key and drive back to the communal meeting spot (probably a campground in Zion Canyon or a motel near the South Entrance); when Group B arrives at Lee Pass, they find the key and also drive back.
Backcountry Camping & Permits
If running 48 miles in a day is not your thing, there are both day-hiking and backpacking options. You can day-hike from vehicle access point to vehicle access point (see “Key Stats,” above). Or you can camp en route at any number of backcountry campsites. Visit the NPS site for more backcountry information (see the links below).
Water is relatively abundant in Zion compared to most of the Colorado Plateau and there are ample opportunities to tank up or top off, especially in the spring when springs and pools are full of snowmelt.
There are at least two permanent water sources en route: La Verkin Creek and the North Fork; there is also a good spigot near the bathrooms at Grotto Trailhead, which will have better water than the North Fork.
Beatty Spring, Potato Hollow Spring, West Rim (Cabin) Spring, and Stave Spring are all mostly reliable, if not permanent.
Hop Valley is flowing most of the year, but this valley is grazed and the water can be foul, so plan to bypass it or plan to purify it.
It is likely that you will find more water sources than mentioned here, especially in the eastern half.