States officer to follow the Lewis and Clark Expedition. With the original intent of opening up the Santa Fe Trail, McClallen was twice deflected from this task by circumstances beyond his control. Instead the mysterious traveler entered the Pacific Northwest, discovered a practicable route across the continent, and for a brief but crucial moment blocked British expansion of trade to the upper Columbia River. As the author demonstrates with careful analysis and painstaking documentation, if McClallen had not taken the bold (and unauthorized) step of unilaterally declaring the United States right to the Pacific Northwest, British interests might have brought a stronger claim to the Columbia River and Pacific Slope south of the forty- ninth parallel. For devotees of American Western history as well as mystery lovers, this book will prove to be engrossing reading.