It has the potential to be huge. You never know what's just under the surface until you look. The NatGeo special, "Ten Years On Mars"[1] made a point to include how when a bad tire on Spirit dug a trench in the soft crust, an unexpected surprise revealed itself.

http://channel.nationalgeographic.com/channel/episodes/ten-y...

Edit: Add pertinent link:

http://www.sciencebuzz.org/blog/accidental_tourist_bad_wheel...