He was also the captain of the Arizona Rangers, warden of Yuma Territorial Prison, and a United States Marshal in San Diego, California.

[1] In 1898, Rynning discovered that the war with Spain had begun and that his old friend, Colonel Leonard Wood, was raising a volunteer cavalry regiment, which later became known as Theodore Roosevelt's Rough Riders.

In 1906, Rynning commanded a large posse of American militia that assisted Colonel Emilio Kosterlitsky in quelling the riot at Cananea, Sonora.

In June, authorities received a telegram from mine owner William D. Greene reporting that American citizens were being attacked by rioting caused by a strike among the workers at the Cananea Consolidated Copper Company.

Placed between the strikers and the office buildings of the Cananea Company, Rynning's men guarded the property during negotiations until asked to leave by Mexican officials several hours later.

[1][3][4] On September 4, 1906, Rynning led Arizona Rangers and immigration officers in a raid on an underground cell of the Partido Liberal Mexicano during a meeting in Douglas.

The Douglas group had also commissioned Javier Huitemea to negotiate with the Yaqui to support them promising the tribe the return of the land which had been taken from them.

Rynning died in San Diego on June 18, 1941, at the age of seventy-five, and was buried at Fort Rosecrans National Cemetery.