Yeah, I'm not sure why some are blurry and some aren't. They're brushes that I made, and are half size, so for example if one brush was normally 231 pixels, I knocked it down to 115 pixels. I'm thinking it's some rastering artifact that wouldn't happen if I was using a vector program.

But after placing all these mountains, now I don't like their look - too pointy. I'm going to go for some rounder, lower, more subtle ones.