I posted this idea quite a while back, somewhere in the many, many posts I've made at this forum. I fear it would take hours for me to try and fine it, so I'll just re-state it.

I had been looking at the orbital imagery and commented that I thought I saw a series of bench-like outcrops along the side of the hill that seemed to border the upslope side of the dark-material field. It looked to me like the benches could be the source of the dark material, since they seemed to be just as dark as the rest of the field. I was arguing that this seemed to be unique material -- much, much darker and less red than everything around it (which, we now see, it surely is).

I proposed that the dark beds could be the eroded remnants of a layer of lacustrine materials, uplfted at the base of the hills. And I thought that made what has now been named El Dorado a prime target for investigation.

I may be wrong about the lacustrine origin, but I'm surely glad we're checking it out! I would also hope that a mini-TES from this spot would be able to characterize the outctops we *do* see at the far extent of the dark sand field as either the source of the dark sand, or definitely *not* its source.

In any event, we need a decent shot at the mineralogy here, to constrain any assumptions on the origin of these sands. Until we get that, this discussion is pretty much in the energetic-arm-waving phase.

However it comes out, this is a very exciting process!

-the other Doug

The individual grains are quite well rounded, which would argue for them having travelled quite a distance and for a long time, unless they were already well rounded before eroding from an outcrop that is nearby. The former is more likely.

I think these could be the transverse aeolian ridges mentioned by Bill, but those come in several flavors as described in the attached paper. If this classification is still in vogue, these appear to be TARs of the "networked" variety. Bourke et al mention the following with regard to that type of TAR:

"Network: Networked ridges in troughs on Mars tend to
form in local topographic lows and areas of secondary
flow circulation. They are closely spaced and appear
to be smaller than the other ridge types (Fig. 1e)."

Granted, they were studying aeolian ridges in the ubiquitous Martian troughs, but this doesn't seem to be too much of a stretch. They are similar to those seen in the bottom of Endurance. It is apparently downwind of the nearest local peak, and other aeolian bedforms in the vicinity seem to be converging on this area. It seems to be a convenient wind shadow in the average local flow that experiences fluctuations. In that light, it is not surprising that it's boundaries are fairly well defined. It looks like secondary flow, or as previously mentioned, something like a vortex.

This is an exciting time and every day brings in new imagery for a new round of arm-waving. Exploratorium has more MIs from yestersol, as well as Hazcams and other images.

Now that Doug mentions it, I recall his comments about the dark area some time ago. Spirit's next stop ought to be those ledges upslope. Tom's paper is a good reference on duneforms.

Here is where she is sniffing...

--Bill

"708 p2267.05 72 0 0 72 2 146 pancam_El_Dorado_pan_L257R2"

I presume that's a 6 x 3 - just what the doctor ordered

MI images of the MB noseprint followed by an APXS integration on 709

Depending on the length of the APXS integ ( perhaps overnight? ) 710 could be a leaving-el-dorado day


Doug

It is remarkable how productive Spirit is these days... How many targets have she investigated in the same time Oppy has been stuck at the same outcrop for over a month now?

Let's hope Oppy will bounce back soon with some kick ass driving

latest pics are down..looking around at the dunes it seems..
ripples

I think it's a 9 x 2, not a 6 x 3 I was close though

Doug

Here's what's down so far (pretty false-color):

Looking at the MI, and while the results don't arrive, the sand in El Dorado looks to be formed from different materials, is it possible to be, I'm repeating myself here, volcanic sand? And if the results indicate basalt and crystals, mainly olivine, and magnetic properties? Will this a definitive proof of it?

Compare this...

http://qt.exploratorium.edu/mars/spirit/mi...00P2977M2M1.JPG

With this...

http://www.microscope-microscope.org/appli...d/CA-Black2.jpg

'California black sand after magnet
Many of the black particles stuck to the magnet. Those metallic particles are called magnetite. I looked at what was left. There was still some black minerals. My guess is that they are hornblende. The green crystals could be olivine.'
http://www.microscope-microscope.org/appli...scopic-sand.htm

Mossbauer and APXS will answer those questions, but it'll be some time before we see them obviously

Doug

Doug, can you tell me, from the code:
706 11:41:12 p2534.15. 1 0 0 13 0 13 13 pancam_Seven_Cities_L234567Rall
where is Seven Cities located? In the Inner Basin or in the El Dorado area?

More of El Dorado:

I'm drooling...We've got a tradition here that is to wear baby blue underwear on the first day of the year but that tone of blue will be more appropiate...

I confess I wasn't that interested in visiting El Dorado. I figured it was just more sand. Well, I was partly right, it is mostly sand, but boy, it is certainly interesting...

I confess I was dying to see those wheels there...
Guess we've followed different paths...I came out of the abyss to contemplate the sun bathing a beautiful Undae, and the non-abyssers found there something, although not unexpected, beautiful...
A GREAT New Year to you and I sincerly hope you continue the amazing work...