Search for a radiation-shielded site in the Mars underground

Radiation in space is one of the most challenging problems for long manned space missions. Recent proposals have been put forward to benefit from natural shielding, by implanting the astronauts’ base in the Martian underground. The Martian caves should be chosen according to some criteria, such as the effectiveness of the shield, the presence of water,… How find the right place for a fast and good installation of the Mars base? This is the question I would like to investigate.