"The Cocheco Railroad (so named because it follows the Cocheco River) was chartered on July 2, 1847. It's original charter was to reach from Dover, NH to Meredith, NH where it would connect to the Boston, Concord and Montreal Railroad. On June of 1848 construction began. Tracks opened from Dover, NH to Farmington, NH on September 21, 1849 and then opened as far as Alton Bay, NH in September of 1851. The Cocheco Railroad never reached it's final destination of Meredith - with Alton Bay being the end of the line. In April of 1863 the Cocheco Railroad reorganized as the Dover and Winnipisogee Railroad and in November of that same year it was leased to the Boston and Maine Railroad. In June of 1892 the Dover and Winnipisogee Railroad was absorbed into the Boston and Maine Railroad."
It appears that the 1870 kml files are in error. The USGS route actually follows the Cocheco River from Dover to Alton Bay.