[cabojoe]

The picture was from over 200 sols ago before the rover went into the crater. I found a few more frames at http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_n115.html if anyone is interested.

[Smokin' Joe]

Thanks, cabojoe, that really helped put the image in perspective.

Looking at the other images, it seems pretty obvious that this is just one of a multitude of rock fragments split and disturbed by the ground bulge from the impact (that formed the crater).

Taken out of context, it looks like a piece of wood lying on mudcracked sediment, but the mudcracked appearance is apparently a result of localized deformation proximal to the crater and caused by the impact. NEAT!

[ancient_geezer]

Ahhh, your link

http://marsrovers.jpl.nasa.gov/gallery/all/opportunity_n115.html

1st row 3rd frame settles it:

 

 

See, Martian Grubworms did it, no doubt about it --------------------------:

From Mars Orbiter Camera 1999-08-11

Fig.1 M04-00291 as isolated for the Enterprise Mission site.