 In 1883 Crook went into the Sierra Madre of Mexico following Geronimo.Sieber was Crook's lead civilian scout and mentor to Tom Horn, whom he taught to speak German, as well as fighting together during the Battle of Cibecue Creek and Big Dry Wash. Sieber was in the field but not present when Geronimo surrendered to Lt Charles B. Gatewood and General Nelson Miles in 1886.Sieber stayed on at San Carlos as Chief of Scouts for another 13 years.