It is one of the longest units of the National Park System in the country. "It," of course, is the Oregon National Historic Trail, which stretches more than 2,100 miles from Missouri to Oregon. It’s been estimated that between 1840 and 1860 some 300,000-400,000 men, women, and children embarked on the four-month-long trip to head to the West Coast. It was long, arduous, and deadly.