The Mammoth Book of Travel in Dangerous Places: North America

First Crossing of America - Alexander Mackenzie
"Endowed by nature with an acquisitive mind and an enterprising spirit", Mackenzie, a Scot engaged in the Canadian fur trade, resolved, as he out it "to test the practicability of penetrating across the continent of America". In 1789 he followed a river (the Mackenzie) to the sea; but it turned out to be the Arctic Ocean. He tried again in 1793 and duly reached the Pacific at Queen Charlotte Sound in what is now British Columbia. Although this was his first recorded overland crossing of the continent, Mackenzie was not given to trumpeting his achievement. In his narrative it passes without celebration and very nearly without mention.

Meeting the Shoshonee - Meriwether Lewis
As Thomas Jefferson's personal secretary, Lewis was chosen to lead the US government's 1804-5 expedition to explore (and to establish US interests) from Mississippi to the Pacific. Travelling up the Missouri river to the continental divide in Montana, Lewis left the main party under his colleague William Clark, and scouted ahead. With everything now dependant on securing the goodwill of the formidable Shoshonee, he showed admirable caution; but the issue was eventually decided by a fortuitous reunion between the Indian wife of one of his men and her long-lost brethren.