There are a couple of ways to reach this cache. You can drive to within 15m of the cache location, or you can bushwhack an overgrown and challenging trail up from the Salton's Brook Marine Interpretation Centre. If you choose the latter route, increase the terain rating of this cache to 4.
The originally posted position was off the mark by a little bit, so I have updated the position given above with the fix taken by Trofeo, the first finder. That fix has been verified as more accurate and will hopefully make your life a little easier! My thanks to Trofeo and Photodork for helping me out with this.
The cache container is an ammo box of dimensions 12"x8"x2" marked with the word 'TREASURE' (I ran out of the sticky letters necessary to spell geocache, and this particular location is pretty far from a 'Business Depot').