You can read up on Mars Direct for more info.

The gist of it is that the Saturn V has enough delta v to get to Mars, on the count of Mars having an atmosphere, which can be used for aerobraking.

Given the capability of reaching Mars with a Saturn V, the rest of the plan revolved around using Apollo hardware, with some modification, for both transport and habitats(re-use of empty stages featured prominently).

Ultimately even if we had hit some roadblock with martian soil or what have you, in an alternate timeline we could have at least sent uncrewed test flights to Mars and back.