Mossy River Rocks - The Umaquah River - near the coast, on the way to Florence Oregon. It's a short hike down to the river, but with the green moss and the golden leaves... wow!The Umpqua River (pronounced /ˈʌmpkwə/, UHMP-kwah, NOT OOMP-kwa) on the Pacific coast of Oregon in the United States is approximately 111 miles (179 km) long. One of the principal rivers of the Oregon coast, it drains an expansive network of valleys in the mountains west of the Cascade Range and south of the Willamette Valley, from which it is separated by the Calapooya Mountains. The "Hundred Valleys of the Umpqua" form the heart of the timber industry of southern Oregon, generally centered on Roseburg. The river and its tributaries flow entirely within Douglas County, which encompasses most of the watershed of the river from the Cascades to the coast.