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Landscape and Climate in the Umpqua Basin

The Umpqua Basin can be divided into three regions based on landscape and climate: the Coast Range, Klamath Mountains, and Cascades regions. The landscape of the Coast Range region is dominated by small mountains and hills. Elevations generally range from sea level at the mouth of the Umpqua River to 2,000 feet. Climate in the Coast Range region is heavily influenced by weather patterns of the Pacific Ocean. Westerly winds carry moisture and warm temperatures inland, resulting in moderate, wet winters and cool, dry summers. In general, temperatures in the winter stay above 40ºF. Summer temperatures are usually are around 70ºF. Precipitation is highest around the mouth of the Umpqua River, ranging from 75 to 80 inches per year. Further inland, the rainfall is around 53 to 60 inches per year.

Much of the Klamath Mountains' landscape is dominated by low interior valleys, broad floodplains, and terraces with gentle to moderate slopes. Elevations are generally between 500 and 1,000 feet.  In the southern part of this region within the Basin, steep mountains with deep, "v"-shaped valleys are more common.  In these areas, elevations are higher, reaching over 2,000 feet in some areas. Temperatures in this region are more variable than in the Coast Range.  Average summer high temperatures are frequently in the mid-70s to 80s, and often reach 90ºF or higher. Winter temperatures are generally in the 30s and 40s, and often drop below freezing. Average precipitation is strongly influenced by elevation. The lowland valleys are generally the driest, with some areas averaging around 30 inches per year and less than one inch per month during the summer; in these areas, it is very common for streams to become dry. As elevations rise, so do precipitation levels.

The entire eastern portion of the Umpqua Basin is within the Cascades region. The landscape is steep with rugged mountains and deep, V-shaped valleys. Elevations in this region are very high, generally between 1,000 and 5,000 feet and reaching a maximum height of 9,182 feet at Mount Thielsen.  High elevations result in cooler temperatures and greater precipitation than the other two regions. Storms blowing in from the west are forced to rise as they encounter the Cascades, causing large amounts of precipitation on the western slopes.  Annual precipitation ranges from 50 to 80 inches, but can reach 90 inches at higher elevations, often in the form of snow.