This article suggests liquid water was involved in avalanche flows in Reull Vallis in the Hellas basin within the last few hundred million years, and perhaps more recently:

Evidence of liquid water in recent debris avalanche on Mars
D. Baratoux, N. Mangold, C. Delacourt, and P. Allemand
"The identification of landforms associated to liquid water on
Mars is a major goal for the understanding of the geologic and
climatic evolution of this planet. In the region of Reull Vallis, near
Hellas basin, lobate debris aprons are recent landforms due to the
creep of water ice mixed with rocks. Among these landforms, one
unusually long debris apron has a tongue-shape and gross
morphology that indicates a different mechanism of deposition.
This study demonstrates, using topographic data from Viking DEM
and MOLA (Mars Observer Laser Altimeter) that the geometric
parameters of this feature support the presence of liquid water
during its flow. This landform is therefore comparable in size to the
most developed wet debris avalanches on Earth. Its late Amazonian
age questions the presence of near-surface liquid water in the recent
geological past of Mars."
Geophysical Research Letters - Vol. 29, No. 7, 1 April 2002

I have argued that recent liquid water on Mars leads to regions of high color variability. One of the regions mentioned was Reull Vallis:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: First color images from 2001 Mars Odyssey?
Newsgroups: alt.sci.planetary, sci.space.history, sci.astro, sci.astro.amateur
Date: 2002-04-19 11:27:49 PST
http://groups.google.com/groups?selm=832ea96d.0204191027.24a301e2@posting.google.com

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Liquid water on Mars and regions of high color variability.
Newsgroups: alt.sci.planetary, sci.space.history, sci.astro, sci.astro.amateur, sci.geo.geology
Date: 2002-07-28 00:58:42 PST
http://groups.google.com/groups?selm=832ea96d.0207272358.2025723a@posting.google.com

Bob Clark