Damn! That's a neat cover... If, as I did, you grew up playing with "Major Matt Mason" (From Mattel), you will not be able to resist this novel of the first manned Mars expedition.
This novel spends half it's time and most of it's energy on the murderous jealousy of the expedition leader who seems ready to kill the other four men in order to have the one woman astronaut for himself... Bit of a failure in the psychological testing there, I'd say.
When the astronauts land on a fairly believably depicted Mars (circa 1962) they strap on their spacesuits and their M-14 rifles - and go forth to meet the strange and hostile Martians. Yep, vegetation and possibly intelligent, if non-humanoid, Martians. Cool!
It's not a good novel by most measures, but I enjoyed it anyway.