The waypoint and the final location are in the upper part of the park in the small landscaped area with ornamental trees and drought tolerant shrubs, paved paths, and benches. The city is trying to deter cyclists from using an unofficial trail that starts in this area, so with any luck you won't have mountain bikers tearing through while you are finding the cache. Be aware of cyclists in the general area, though; segments of the Fullerton Loop mountain bike route go through this neighborhood, including a street crossing within a couple hundred feet of the cache.
At the posted coordinates you'll find painted rocks that a local Girl Scout troop placed around one of the trees. On the west (non-street) side of the tree, you'll find the 4-digit troop number painted on four rocks. Enter that 4 digit number into Certitude to get the final coordinates. The final is nearby. Street parking is available; street sweeping in the neighborhood is on Thursdays.
You can validate your puzzle solution with certitude.