Crossing the icy Delaware River on Christmas night, 1776, allowed George Washington to surprise the British at Trenton, a critical American victory in the Revolutionary War. One of the world's most recognizable natural landmarks, the Grand Canyon, defies the imaginations of the five million people who visit there annually. Pioneer Daniel Boone blazed the Wilderness Trail through Kentucky in 1775 and tamed the wild frontier. The opening of "The Unassigned Lands" in Oklahoma resulted in 50,000 settlers racing across the prairie to grab a stake and claim ownership of a homestead. The discovery of oil in Prudhoe Bay, Alaska, in 1975 called for an ingenious feat of engineering to transport fuel across 800 miles of icy wilderness.