What would you say this is?

When looking at the other pics on the page you posted, I found this pic interesting...

marsrovers.jpl.nasa.gov... ress/opportunity/20040524a/site_B115_navcam_180_cyl_L-B118R1.jpg

I'm not one to look at these pics and try to claim that there's anomalious items, but that sure looks like a big piece of wood. At first I thought it's a rock. But there aren't any other rocks of this color or shape. Looks like a rail road tie. Not that it is. Also, what's that reflecting in the background? Is that the heat sheild? Just caught my eye.

It looks like the coolest parts are those in the shade, particularly near the steep bits of exposed rock. It looks like the temperature drops off pretty quick when the sun goes in. 6 degree C is warmer than I realised, although I think I read somewhere that water on Mars would still evaporate at that temperature due to the low atmospheric pressure.

Still... 6 degrees. The lasses round here wear mini-skirts in colder temperatures than that that!(bless 'em)

The surface temp of Mars can get up to 80 degrees F.
AT the equatorial regions.Where the ground can hold the heat.

BUT, thats literally AT the surface...just a few inches above that, it will be
MUCH MUCH colder.. It's a lot like the moon, in a way, where the shadows
will be below zero, but inches away in the sunlight it's DANG HOT.

THere is a little convection in the "air" on Mars to carry some heat around.
So the differences between Shade and Sun, are not as drastic..

Ah.. so the differences in temperature near the exposed rocks is due to the the nature or makeup of the rocks themselves, rather than the fact they are just shading something.

So.. that means the the underlying rocks are probably extremely cold all the time, whereas the surface dust/sand can heat up in the sunlight and then retain a bit more heat?

Interesting.