A team from the USGS Astrogeology Branch in Flagstaff report finding columnar jointing in near surface rocks on Mars, indicative of cooling lava and liquid water. The jointing was identified on photos from the UA HiRISE camera on the Mars Reconnaissance Orbiter.
The caption in the Geology article describes: HiRISE image PSP_005917_2020 . Columnar jointing is seen in rocky outcrops that were exposed and tilted during formation of the crater. North is up and to right. A: The most well-exposed columns are seen in this outcrop. Columns are ~25–30 m long and 2 m wide. B: At the base of the outcrop we see fanning and radiating columns <1 m wide . C: Thin, fanning columns, probably entablature, are also visible in this outcrop. Scale bars are only valid in horizontal direction due to foreshortening of cliffs.
Ref: Discovery of columnar jointing on Mars, M.P. Milazzo,*, L.P. Keszthelyi, W.L. Jaeger, M. Rosiek, S. Mattson, C. Verba, R.A. Beyer, P.E. Geissler, A.S. McEwen and the HiRISE Team, Geology, February 2009, v. 37, no. 2, p. 171-174, doi:10.1130/G25187A.1, http://geology.gsapubs.org/cgi/content/full/37/2/171