Here is an article on the preliminary results from Mars Odyssey’s radiation environment experiment.
The image shows pretty much what one would expect, I suppose — that cosmic ray intensity is higher at higer elevations like the Tharsis volcanoes and lower at lower elevations such as Hellas.
The interesting part is that the entire range (10-20rem annualized) is lower than that for the ISS (20-40rem annualized).
Yet another way in which planetary settlements beat orbiting colonies.