20 years after publication, "The Surface of Mars" is still the absolute best starting point for anyone interested in learning the basics about what Mars is like. Chapters describe the channels, craters, volcanoes, history, moons, etc. as best as these topics were understood at the end of the 1970s Viking missions. Even after Pathfinder and with Mars Global Surveyor, this is still the book I suggest people start with to learn about the Red Planet.