In the book Into the Wild, why does Chris McCandless abandon the Datsun, and why was the discovery of the car important?

In the book Into the Wild, Chris McCandless abandons his Datsun after a flash flood hits Lake Mead, Nevada. When McCandless realizes that his wet battery will prevent him from diving further west without seeking help, he abandons his car by the side of the road, hides his license plates and remaining cash, and begins hitchhiking. He spends the following two months hitchhiking all over the west coast, working briefly on a ranch in California.

Finding the Datsun becomes important to the story when a National Park Service ranger finds it and reports the vehicle missing. When McCandless's parents hired a private investigator, he was able to find Chris in Oregon through the report of the missing car as well as a hitchhiking ticket he had received months earlier.