In the 1700s a vast network of "grease trails" stretched from Alaska to the Fraser River, even crossing the northern Rockies. These ancient Grease Trails later formed part of the Dalton Trail, a toll road that opened up the interior of Alaska to prospectors during the Klondike Gold Rush. The name "Grease Trail" was given to these travel routes, because the most important trade item carried over them was grease made from a tiny smelt-like fish called ooligan.