headwaters

noun

1. (plural, plural-only)The source of a river, the set of streams that feed into the river's beginning.

   “... but when his brows began to wrinkle with time, and he stood alone, the last of his family, and his particular tribe, the few Delawares, who yet continued about the head-waters of their river, gave him the mournful appellation of Mohegan.”

   “Driver Thornhill beckoned me across the cab and pointed out some two miles ahead as we looked across the headwaters of the Eden Valley, the summit cabin at Ais Gill itself, with the summit point and altitude conspicuously indicated.”