High Quality Content by WIKIPEDIA articles! The yellowfin cutthroat trout (Oncorhynchus clarki macdonald), a subspecies of the cutthroat trout, was officially identified in 1891 and named after the US Fish Commissioner, MacDonald. The yellowfin cutthroat is extinct. At the end of the last ice-age boulders and clay moraine blocked off a tributary of the headwaters of the Arkansas River in what is now the state of Colorado. The two lakes which formed were named the "Twin Lakes" by the area's settlers. Both lakes held small greenback cutthroat trout from the early days of the Wild West, but in the mid-1880s reports circulated of much larger trout, up to 10 pounds (5 kg) in weight, with bright yellow fins. In July 1889, Professor D. S. Jordan and G. R. Fisher visited Twin Lakes and published their discoveries in the 1891 Bulletin of the United States Fish Commission.