Years before my journey through the valley of the Ka-Ho-Nee, which has made my passage through time less troublesome, I was a young lad and lived near where Oceanside is today. During very low tides, my brother and I liked to go down the beach and play by a cave that went through the headland. One time, we stayed too long and got cut off by the tide, and had to wait nearly a whole day before the tide went down enough to get out again. When we got back home, we found that our parents had turned out the whole area to look for us. Let's just say that we weren't able to sit down for a while...
Our family left the area shortly after that, and in all my wanderings, I'd never made it back there until recently. Things have changed a great deal, but the cave is still there. Apparently it is called "Lost Boy Cave"; I doubt they named it after me, but what the heck. 
You can get to this cache heading north up the beach from Oceanside, but the best way to approach is to park near N 45 28.374 W 123 58.137, and take the public trail down to the beach, and head south. There is an unusual waterfall there that could be interesting to some. The cave is just around the point, and has two entrances from this direction. Unless the tide is really really low, you'll need to go through the cave to get to the beach on the far side. It only needs to be really low to get through the cave. 
Under the right circumstances, the terrain rating on this cache is two stars. Most of the time, it will be four plus to five stars. Timing is critical. Be sure to leave time to find the cache and get out before the tide returns.