They have a Quicktime movie up made up from pictures from Opportunity
showing the rover getting itself unstuck from the dune:
http://www.jpl.nasa.gov/videos/mer/0...pportunity.mov
Whoever designed those wheels the way they did should get a medal, as
the rover doesn't drive its way out, it _digs_ its way out using the
wheels like bucket-wheel excavators. One thing this movie really lets
you see is the consistency of the Mars soil, and how it behaves when
acted on by mechanical force; to me the way it behaves is a lot like I'd
expect Lunar soil to behave- it's got a decided "stickiness" to it and
stays clumped together, as well as adheres to things when compressed,
the way dry cement dust would. The appearance of the soil in the wheel
cleats makes it looks like it's extremely homogenous and fine grained,
but has a sort of fragile crust over its surface that the rover is
grinding up with its wheels, like very fine-grained sand whose surface
has been wetted and then allowed to dry.

Pat