The cache is not at the posted coordinates. It is a bonus available after completing the Adventure: Fourth Street: Art of Burning Man.
This cache is found by completing the Adventure: Fourth Street: Art of Burning Man. That Adventure starts at any of a handful of locations on the south side of Fourth Street. (Fourth Street is just north of the question mark for this cache on the geocaching map. The Adventure Lab logo for the Adventure is east of that question mark, at Fourth and West Streets.)
Upon correctly answering the questions associated with each location of the Adventure, Adventurers will obtain numbers representing V, W, X, Y and Z. Substitute the corresponding numbers into the following formula to determine the bonus cache coordinates.
Bonus cache coordinates: N39 31.(X + Z) (X - Z) (X/2) W119 49.(V/2 + W) ({Y-X}/2) ({W-V}/2)
Accessibility: This bonus cache is wheelchair accessible, but wheelchair Adventurers will find some questions more challenging than will those with greater mobility. I welcome and wish for feedback from wheelchair Adventurers.