RE: drainage ?
A drainage can be a wide variety of things. For example, the Green River drainage is any river that eventually flows into the Green River. With that in mind, some can be huge, some can be very small. In the field, most people I know refer to drainages like they do rivers or streams or a groups of canyons and streams that represent a drainage.i.e. 3 canyons we hunt make up the South Fork Drainage and that's how everyone around here knows the area, etc.