In the desert when Ron drops Chris off at his camp, Chris hops up onto the hood of Ron's truck. This happens almost immediately after they pull up. Chris should have burned his hands and legs on the hot metal of the hood of the truck, as the engine beneath would still be hot.
In the night scene, with the Las Vegas strip in the background, the Stratosphere Tower can be seen on the right side of the screen. The scene takes place in the early 1990s; the Stratosphere was completed in 1996.
In the graduation scene at Emory, a female graduate is moving through a row of graduates to take her seat. In her hand is a small silver cell phone. In the row in front of her was another female graduate talking on a small cell phone. This technology was not available in 1990.
After Chris leaves Slab City there is a Union Pacific locomotive that runs beside the highway. That locomotive has an American flag painted on the side. Union Pacific did not paint American Flags on their locomotives until the 2000s.
When Chris' parents drive down to Atlanta to see him, Exit 91 for "DeKalb-Peachtree Airport, Emory University" on Interstate 85 is visible. Although, this is the correct exit for Emory, the exit number is incorrect for 1990. Exit 91 is the new, distance based exit number. Georgia used sequential exit numbers until 2000. In 1990 the correct exit would have been Exit 32.
When Chris catches a ride with a trucker, a yellow sticker in the windshield bearing the number "6" is visible. This is a CVSA inspection sticker that indicates the truck passed a safety inspection in 2006.
In the Atlanta scenes, the Bank of America Plaza tower can be seen in the skyline. Construction on this building didn't begin until 1991 and it was not completed until 1992, but these scenes took place in 1990.
When Braves fans come into the place where he and his family are celebrating his graduation, they cheer about the tomahawk chop. Braves fans did not start doing the tomahawk chop until 1991. Chris graduated in 1990.
When Chris is driving the combine in the wheat field and shoveling grain out of the truck, his boss is talking about wheat and the price of the wheat, presumably the wheat they are unloading, Chris is, in fact, shoveling corn.
During the graduation scene, there is a brief shot of an Emory official straightening the black tassels on a couple of graduates' mortarboards. In all other shots, every student is wearing a gold tassel.
During one of the scenes where Christopher is living near the Salton Sea and training, a portion of a bounce-board reflector can clearly be seen in the reflection of one of the windows of Hal Holbrook's vehicle, as Hal watches him from below.
The Park Ranger's uniform in the Grand Canyon kayak scene is incorrect. The uniform colors of green and gray are for a National Park Service ranger. The patch on his arm appears to be for the National Park Service, but is the incorrect patch for the service. Also the badge he wears is the badge of the U.S. Forest Service.
Carine describes that she knew what Chris was doing by getting away after spending four years in college. However, the regalia Chris was wearing at the graduation ceremony is that of someone receiving a master's degree, which would normally require at least another year of coursework.
When Chris is leaving Atlanta to drive West, his Nissan is driving Eastbound on the Freedom Parkway. Furthermore, the Parkway was a dead end and remained incomplete until after the city was awarded the 1996 Olympics in the Fall of 1990, which was after the story took place. The Parkway as it is seen in the film didn't exist at the time of which the story took place.
When Christopher abandons his car, he removes the license plates, VA UW4-924, and throws them away. A few scenes later, when the parents decide to make a surprise trip to Atlanta, that license number is on the family car.