There are lots of dunes on the right (red oval) and another sparser patch on the left (red oval). We happen to be looking straight down the length of the dunes, so we see then as narrow pointy hills. I've used red lines to connect features in the overhead and ground shots.

This is the un-graffiti'd version:

Clearly, Spirit will have lots to do when it arrives at the Columbia hills, including measuring the cohesion of these dunes and their particle size - that will tell us alot about the sorts of wind that were needed to mobilise them, and hence whether the atmosphere of mars was thicker in the relatively recent past, or not.