I just recently found my 100th cache in Hollister Hills SVRA and decided to place the first challenge cache there. The original idea was to have the requirement be finding the exact same set of caches, but that is not allowed according to the current Geocaching Challenge Cache Guidelines, so instead the challenge is simply to find 101 caches with the 'Off-Road Vehicles' attribute. Any cache you have found with this attribute, found any time and whether or not it's archived or currently disabled counts towards the challenge requirements.
Note: There is a $5 daily fee to use the SVRA — cheaper than an amusement park and way more fun!
Congratulations to DragonsWest, Seek2FindMe & Geokashers for Co-FTF.