Imperial Jasper is mined over a wide area in Mexico. There are several variants as described by where in the vicinity it is found. For example, the Royal Imperial Jasper is a nodule-type that is simply found in a different canyon than the other stuff.
It's a beautiful, porcelain-grade jasper with interesting colors and lines. It is similar to Willow Creek jasper but with bolder coloration. I'm always on the lookout for good deals on this at the gem & mineral shows. I'm told that it is plentiful where it is mined, but squabbles between adjacent land owners make it difficult to get.