Forgive me if I'm mistaken but, based on a few of his other posts, I'm not so sure kaiyouw is a mapper. Anything specialized you make at his request is most likely something that he's merely hoping someone else will use. (Again, please forgive me if I'm mistaken.)
I would say anything that fits a western or mexican landscape would work. Maybe some landscapes that appear forested too? Check photos online for Utah, Nevada, Mexico, Arizona, California, Montana, Nebraska, Wyoming, the Dakotas, etc.
I'd also like just a plain blue sky with a sun that's straight up. No terrain. This would be for a deep canyon style map where even spectators won't be able to see above the cliffs. A starry night version of such a sky would be appreciated as well. Probably with a full moon would be great.