This article seems to be lamenting the lack of key discoveries by the
Spirit rover compared to the Opportunity rover:

Mars Water Past Still Mysterious
by Phil Berardelli
Washington (UPI) Apr 16, 2004
http://www.spacedaily.com/news/mars-mers-04zzzv.html

I wanted Spirit to at least drive to the far side rim of Bonneville
to get a closer look at the dark material on the far side of
Bonneville:

Spirit, Sol 84

Mini-TES observations from a distance showed it to have the same
composition as dark material in the subsurface of Humphrey rock:

MARS EXPLORATION ROVERS UPDATE
Spirit Returns Color Panorama of Bonneville Crater
Opportunity Finds 'Blueberries' Are Loaded with Hematite
By A.J.S. Rayl
20 March 2004
http://www.planetary.org/news/2004/mer-update_04-03-20.html

This mystery material was either a glassy silica or a weathered
basalt. This is similar to the mystery material known to make up much
of Mars northern hemisphere from TES measurements, which is believed
to be either an andesite or a liquid water altered basalt. The rover
might have been able to decide between these two possibilities.
Rover scientists did not want to chance driving into the crater. But
as you can see from the Sol 84 image, this dark material extends far
enough up the sides the rover probably could have gotten a good look
at this material without going down into the crater.
However, later images of the Columbia hills show similar dark material
partially up the sides of the hills and in the region between the
hills and Spirit:

Spirit, Sol 91

So it might still be possible to determine the composition of this
dark material.

Additionally, Natalie Cabrol an expert on Gusev Crater where Spirit
landed, has argued there may be frost mounds in Gusev:

Title: Perennial frost mounds in Gusev crater (Mars)
Authors: Cabrol, N. A.; Grin, E. A.; Pollard, W. H.
Journal: Conference Paper, 28th Annual Lunar and Planetary Science
Conference, p. 193.
Publication Date: 03/1997
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997LPI....28..193C

Title: Possible Frost Mounds in an Ancient Martian Lake Bed
Authors: Cabrol, Nathalie A.; Grin, Edmond A.; Pollard, Wayne H.
Journal: Icarus, Volume 145, Issue Icarus, pp. 91-107.
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?2000Icar..145...91C

In her examples taken from MOC images of Gusev, some of the proposed
frost mounds have a sinuous shape not just a conical shape. Then these
could match the shape of the Columbia Hills.
The areas where the proposed frost mounds lie also include the
Columbia Hills.

c.f.:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Mystery material in the Bonneville crater on Mars.
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology, sci.geo.mineralogy
Date: 2004-03-20 05:50:12 PST
http://groups.google.com/groups?th=4005c8b6bfcc019a

Bob Clark