Complex sentence: He traveled extensively throughout the United States in connection with his work, and in 1870 made a survey, along with A. D. Wilson, of Mount Rainier, the highest and most inaccessible peak in the Cascade Range.
Split into simpler sentences: He traveled extensively throughout the United States in connection with his work, and in 1870 made a survey, along with Mr. A.D. Wilson, of Mount Rainier. This is the highest and most inaccessible peak in the Cascade Range.