Cheshire Cat! Clue 7 and a Question

Clue 7: Boulder Creek, which is only a few miles away, has a smaller drainage basin than the stream draining the Quartzville town site area, and is a perennial stream- that is, it always has at least a small amount of water flowing in it, even during the driest summers. (If you click on the arrow on the upper right corner of that map, Canal Creek and the quarry will be in the upper right- NE- of the following map location)

Question: What does the shape and orientation of the columnar jointing in the "grin" tell you about the nature of the cooling surface of this flow?

Clue 8, which I'll try to get up between 5 and 6 PM PDT, will be a crude sketch of the bedrock units exposed along the cliff face in the neighborhood of the quarry, on the opposite side of the road from Canal Creek. Unfortunately, I didn't think to get any photos to illustrate the bedrock relationships here.

Addendum: Dana has a post linking the clues and puzzle, with some additional photos.