The Willamette Valley stretches over 200 miles north-to-south along the Willamette River in Western Oregon. Cradled by mountain ranges to the east and west, the valley branches out northwards from the mountains outside of Eugene up through Salem and then past Portland, where the Willamette River meets the Columbia River at the Washington border. The valley is renowned for its rich and fertile soil, a result of volcanic glacial deposits from the Missoula Floods at the end of the last ice age, and the area is world-famous for its lush, old-growth forests as well as its agricultural output. The Willamette Valley is also world-famous for its prevalence and severity of hay-fever allergies. The valley registers the highest grass pollen counts in the nation on a regular basis, and it was recently stated that Eugene in particular has the highest grass pollen counts in the world. The severity of the pollen varies seasonally as well as yearly, but its especially high throughout May and June, and on the worst days many do not even leave their house due to breathing difficulties.