I hiked the PCT and the Lodgepole trail last weekend, and I found these weird holes in a rock on the PCT just west of Olallie Lake at an overlook area.  It certainly looks man made, but I have no idea what it might have been for.  The area between the holes was 18-24" or so:

I know exactly where you were. Have seen them too. In other areas, I would have guessed, blasting holes, for trail construction.  But that area didn't strike me as needing blasting.  

Did you happen to walk past Lower Lake, or pass it by on the Lodgepole? We were camped at that end of the lake this weekend.

I did.  I was with my dog, and we stopped at Lower Lake and cooled off a bit.  He laid down in it and I took my boots off and cooled my feet a bit. I'd love to know what those holes were for.  I can't imagine what would have needed blasting in that area.  I was thinking it was for some sort of tripod thing, but I have no idea what.