Wilflower requires you to use a mountain bike frame with knobbies.
The course is not technical in any great sense - about a third of the sprint distance is on paved roads (which you be sharing with the long course road bikes). The dirt portion is mostly well-graded fire roads or bike/hike paths that run around the lake area.
As for where Wildflower is held - Lake Nacimiento located west/northwest of the town of Paso Robles in Central California.