Serisously! It was so obvious to me that the petroglyph was a map. Here we have possibly one of the best law men ever, Cooper that is, and he can't even think for a second it's a map. This is the guy who noticed the faint reflection of a motorcycle in Laura Palmers eye, and he can't tell a freaking map?! It's a little inconsistent with the character i think.
It was obvious to me too, but I wasn't really surprised Cooper didn't get it.
What I'm getting at is: is Cooper really that good? He's amazing in some respects, with razor-sharp insights. But he doesn't even really question Leland's bizarre behaviour, a lot of clues pass him by, and he needs a lot of help from the Giant to get to BOB, and then it's after he strikes again. Not really the pinnacle of detective work. Wouldn't it be standard procedure to check Leo's alibi for the night Teresa Banks was killed? Instead he researches Leo's illegal u-turns.
Cooper's detective work is wildly variable and unreliable, in my view. But that could be a thread in itself.
"What credit card do you want to put that on?"
"Caash, prease."