NASA file:
http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=1514MR0077060010204628E01_DXXX&s=1514
reddit pix with inset:
https://i.redditmedia.com/Hi-sy8cPF0aRytrdNVyfgFAPVYNHgGGocmAIxjRlA8Y.jpg?w=860&s=df427058f43560550998da5b3df6190e
May be a geological version of the infinite monkey theorem but, still, wtf?
That's definitely an interesting formation. It could be that magma behaves differently in lower gravity and it more likely to form into cubic pattens as it cools -- or there is something about the chemical composition on Mars that makes it more likely.