[/caption]
The HiRISE camera on the Mars Reconnaissance Orbiter took an image of a thin channel, and a portion of it contains a naturally occurring bridge over the chasm. Kelly Kolb from the HiRISE team says it is probably a remnant of the original surface, the rest of which has collapsed downward. It isn't likely there's a opening underneath the formation, but if there were, it would look very similar to a rock bridge formation found in Jordan in the Wadi Rum, the Valley of the Moon. See an image below.
Kolb also said this is unlikely to be a channel formed by a running water, as there are no obvious source or deposit regions. The channel is probably a just a collapse feature.
And see the full HiRISE image of the thin channel, found in Mars northern hemisphere between some "knobs" called Tartarus Colles, below.
[caption id="attachment_79548" align="aligncenter" width="400" caption="Any chance the Mars rockbridge could look like this one in Wadi Rum, Jordan -- also known as the Valley of the Moon?"]
[/caption]
[caption id="attachment_79547" align="aligncenter" width="580" caption="Small Winding Channel in Tartarus Colles. Credit: NASA/JPL/University of Arizona"]
[/caption]
For more information about this image on Mars,
see the HiRISE website.