The Trans-Zion was apparently first done in a single day in the early 1990s by Terry Tucker. The idea was picked up by Bo Beck, and dubbed the "Far Far Fest". Beck and friends have made the trek several times, and in both directions. Beck's fastest time is 14h25m, set April 28, 2007 (west to east).
Last Trans Zion I did was solo and unsupported. Carried 3 gallons of water and some Protein Bars. Stopped halfway ( At 7 Hours, trying for 14 hours.) .Missed my goal of 14 hours by 25 Minutes.