A passing driver told border patrol agents that two cars heading north, with Mexicali license plates, had just made U-turns on the highway shortly before the checkpoint. Two agents in marked cars headed south to investigate. Approximately one minute later (and about one mile from the checkpoint), the two agents saw a blue Chevrolet Blazer and a red Nissan sedan, both with Mexicali plates, pull off the shoulder and re-enter the highway heading south. It is well known that the area where they first observed the cars is used by lawbreakers to drop off and pick up undocumented aliens and illegal drugs while evading inspection. The location is also the only place where it is feasible to turn around both safely and with impunity. After that point, the road narrows and is in plain view of the checkpoint. Both agents testified that almost all of the stops made by the Border Patrol at the turnaround site resulted in the discovery of 'a violation of some sort . . . ' involving either illegal aliens or narcotics. Agent Johnson testified that the majority of people going through the El Centro checkpoint are Hispanic. Hispanics make up roughly 73% of the population. Agent Johnson also testified that as he pulled behind the Blazer, he noted that both the driver and the passenger appeared to be Hispanic. Johnson stated that when the driver and passenger noticed him behind them, the passenger picked up a newspaper and began reading. This, according to Agent Johnson, further aroused his suspicions. Johnson then stopped the Blazer, identified himself as a Border Patrol agent, and asked about the citizenship of the two occupants. The driver, Lorenzo Sanchez-Guillen, and his passenger, Sylvia Renteria-Wolff, showed Agent Johnson I-586 cards, which allow Mexican citizens to travel up to 25 miles inside the United States for no longer than 72 hours at a time. As the Blazer had been stopped approximately 50 miles from the border, Johnson then brought the two occupants to the checkpoint for processing. Agent Fisher continued to follow the second car, a red Nissan sedan. As Fisher caught up with the vehicle, he could see that the second driver also appeared to be Hispanic. Fisher ultimately pulled the Nissan over after following it for approximately four miles. D was the driver. After stopping the car, Agent Fisher, with the aid of Agent Johnson, who had returned to help him, searched the trunk and found two large bags of marijuana. A subsequent search of the Blazer back at the checkpoint turned up a loaded .32 caliber pistol in the glove compartment and an ammunition clip that fit the pistol in the passenger's purse. D, Sanchez-Guillen, and Renteria-Wolff were charged with conspiracy to possess marijuana with intent to distribute, and possession of marijuana with intent to distribute in violation and Sanchez-Guillen was also charged with being an illegal alien in possession of ammunition. Ds filed a pre-trial motion to suppress on the ground that the vehicle stop was not based on reasonable suspicion. The district court denied the motion. Ds were tried or entered a conditional guilty plea and all appealed.