Potomac River kouri sou 383 mil de Fairfax Stone, West Virginia pou Point Lookout, Maryland. Li afekte plis pase 6 milyon moun k ap viv nan basen vèsan potomak, zòn nan 14,670 kare kilomèt kote dlo a bwè nan bouch rivyè a. Kat jeyografik sa a montre kote rivyè a ak zòn basen vèsan li yo ki kouvri atravè plizyè rejyon jewolojik ki gen ladan Plato Appalachian, Ridge & Valleys, Blue Ridge, Piedmont, ak Kòt Plain.
Tij prensipal la plis tout tributaries pi gwo total 12,878.8 mil fè Potomac larivyè a 21yèm pi gwo nan Etazini yo. Tributaries prensipal yo nan Rivyè Potomac se North Branch, Rivyè Savage, South Branch, Cacapon, Shenandoah, Antietam Creek, Monocacy River, ak Anacostia River. Potomac an empties antre nan Chesapeake Bay en.