A test question I will never forget from a Montana Geography class I took is that the source of the Yellowstone River is a trickle on Younts Peak. That answer has followed me to every river, stream or backyard ditch I have gandered upon ever since: Where is its source?
The source of a river is defined as the original point from which the river flows. Yet this is one of those instances where the dictionary leaves you knowing less than when you started. Is it the furthest reach of the stream itself, and goes no further than the confluence of tributaries that result in the actual named feature? Does it have to be perennial, or do intermittent streams count? What of ephemeral drainages, like those that run full when the gully washers of June pour over the Continental Divide?
The primary drainage of northern Jefferson County is Prickly Pear Creek, which consolidates the catchments of the northern Elkhorns and Boulder Mountains and guides them to the Missouri River. As a 10-year-old kid trying to hook a brookie near Clancy, I could look south to Elkhorn Peak and its volcanic silhouette and know that the water I stood in came from somewhere up there. In fact, the furthest reaches of Prickly Pear Creek can be found in the snowmelt-fed springs of Rabbit Gulch, high on the northern flank of Elkhorn Peak.
