 This caused some confusion when the specimens were first examined in the 1870s by Edward Drinker Cope, who first identified them as greenbacks, since the river does not flow through anywhere in Kansas.Two decades later, David Starr Jordan, one of the leading ichthyologists of his day, resolved the apparent impossibility by deciding that Hammond must have collected them on a trip to Fort Bridger, in the Green River basin in southwestern Wyoming, which would have likely taken him along the South Platte.Although the greenback cutthroat was considered extinct by the 1930s, in 1957 a population was discovered in Rocky Mountain National Park in the Big Thompson River, a tributary of the South Platte.