Soon, his brother was also released and the two soon hooked up with Richard "Rattlesnake Dick" Barter, who had formed a gang that "worked” the Sierra foothills, relieving muleskinners of their loads of gold coming from Nevada City, California. In 1856, when Barter learned from a drunken mining engineer that a large gold shipment was going to be sent down Trinity Mountain from the Yreka and Klamath River Mines, he sent George Skinner and three others to intercept the shipment. The four bandits were extremely successful, stopping the mule train outside of Nevada City and demanding the gold at gunpoint. Meekly, the billion was turned over without a shot being fired.

George and the rest of the bandits then began to make their way to Folsom where they were to meet Barter and Cy Skinner. However, they quickly found it next to impossible to take the heavy gold shipment down the mountain passes without fresh mules. Soon, they split up the gold shipment, burying half of it in the mountains, and taking the rest of it with them. As they made their way to Auburn, the thieves were intercepted by a Wells Fargo posse and a gunfight ensued. In the melee, George Skinner was killed and his confederates fled. The lawmen recovered $40,600 of the stolen loot and though they searched diligently, they failed to find the remaining $40,000.

Both men soon went back to robbing stagecoaches but their luck ran out on July 11, 1859, when the pair were trapped in a mountain pass by Sheriff J. Boggs. When the outlaws resisted, Boggs shot Rattlesnake Dick, killing him instantly and Skinner was wounded. However, he would live to once again be sent to San Quentin. There, he made the acquaintance of Henry Plummer, who was serving time for second degree murder. The two would become friends, and would later "hook up” again in Idaho.

Many who believed that Plummer had acted in self-defense, petitioned the governor, and he was released in August, 1859. Though Skinner was to spend 15 years in prison, he once again managed to escape in May, 1860 and fled north to the gold camps of Idaho. In January, 1862, he ran into Henry Plummer in Lewiston and the pair were said to have then formed a gang of road agents, which included such men as "Clubfoot" George Lane and Bill Bunton, robbing travelers of their personal possessions and relieving stage and freight companies of their gold shipments. Soon, Idaho citizens were becoming suspicious of the men, who then made their way to the gold fields of Montana. There, Skinner established a saloon in Bannack and another in Virginia City. With his profits, he began to invest in mining claims, and soon found himself a "wealthy man.” He then met and married a woman named Nellie, who some said married him only for his money.