Mason is the remains of a lunar impact crater that lies in the northeastern part of the Moon.

Along the northern rim of Mason is the southern edge of the Lacus Mortis, a small lunar mare.

This is a heavily eroded crater formation that is somewhat irregular in shape, being longer in the east–west direction.

The rim is an uneven, disintegrated ring of ridges that have merged with the rough terrain to the south and east.

[1] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Mason.