Three years later, Mosher accepted an assistant professorship at Stanford University in the Department of Chemistry, and he and his wife moved to California for the position.
He and his graduate student Melanchton Brown identified a deadly toxin produced by the California newt living in Stanford's Lake Lagunita, calling it tarichatoxin.
They soon discovered that it was the same toxin produced by the puffer fish, used in a rare type of sushi that if prepared incorrectly could paralyze and kill human diners.
Harry Mosher served as chair of the California section of the American Chemical Society in 1955 and on the ACS National Council, both elected positions.
He spent his later life engaged in tennis and skiing, and lunched regularly with his friends at the Rathskeller in the Stanford Faculty Club.