After weeks of tramping the American Southwest following his graduation from Emory University, Christopher McCandless arrives at the town of Topock, Arizona. There, he impulsively buys a secondhand aluminum canoe, and begins to paddle down the Colorado River to the Gulf of Califormia. The lower Colorado passes through "some of the hottest, starkest country on the continent," and McCandless is "stirred by the austerity of the landscape." From Topock, he travels south down Lake Havasu, through the Colorado River Indian Reservation, the Cibola and Imperial National Wildlife Refuges, and the U.S. Army's highly restricted Yuma Proving Ground. McCandless stops briefly in Yuma to replenish his supplies, then continues south. Carrying no identification, he sneaks into Mexico by slipping through the open floodgates of the Morelos Dam, then becomes hopelessly lost in a maze of irrigation canals. After alternately paddling and portaging for days, McCandless is fortunate to run into some duck hunters who speak English. These kind men tow him to their base camp, and then drive him and his canoe to El Golfo de Santa Clara, a fishing village on the Gulf of California. From there, McCandless again takes to the sea, traveling south along the eastern edge of the gulf.
McCandless had begun his journey by canoe at the end of October, and it is now the first week in January. At this time he is caught in a violent storm which sweeps his little canoe out to open waters, and he barely escapes with his life. This close call convinces McCandless to abandon his canoe and head back north. Leaving the boat southeast of El Golfo de Santa Clara, he begins walking north along the beach, is caught by immigration officials at the United States border, and is briefly incarcerated (Chapter 4).