In 1794, Gass moved to Mercersburg, Pa, and became a carpenter's apprentice for two years. During that time, he worked on a variety of projects, including James Buchanan, Sr.'s home. During that project, Gass became acquainted with "little Jimmy," the future president of the United States(1857-1861).
In 1803, while enlisted in the army, he took the opportunity to join Lewis and Clark. Gass volunteered, along with John Ordway and Charles Floyd. While on the trip, Gass maintained a journal, but his poor education hindered his ability to write and express the events of the day well on paper. He joined as a private, but was promoted to sergeant after Charles Floyd died.
When the expedition returned in 1806, Gass's friends encouraged him to publish his journal. Understanding that he lacked the skill to edit and make the composition comprehensible for the general reading public, Gass approached a schoolteacher, David McKeehan, to prepare the record for printing. McKeehan agreed, and the pair decided that Gass would receive 100 copies of the final work, and own the copyright. The balance of the printed editions would belong to McKeehan. Zadok Cramer published the book. Markets and timing proved kind to Mr. McKeehan, as the country was excited to read about the newly returned expedition and the discoveries and knowledge the explorers brought back. The Gass edition of the Lewis and Clark Journals enjoyed several printings within the United States as well as translations into German and French, and printings in England. The editions printed from Clark and Lewis's papers would not be published for another seven years.