few horses from the 5th Cavalry. Shannon and the Apaches found the rebels' trail, which was a week old by then, and followed it for some time until finally catching up with the Mexicans near Las Varas Pass, about forty miles south of Namiquipa. Using the cover of darkness, Shannon and his scouts attacked the Villistas' hideout, killing one of them and wounding another without losses to themselves. The Villista who died was thought to be the leader as he carried a sword during the fight. Another skirmish was fought on June 9, north of Pershing's headquarters and the city of Chihuahua. Twenty men from the 13th Cavalry encountered an equally small force of Villistas and chased them through Santa Clara Canyon. Three of the Mexicans were killed and the rest escaped. There were no American casualties. End of active operations On May 9, at a face-to-face meeting in El Paso, Texas, Carranza's Secretary of War and Navy, General Álvaro Obregón, threatened to send a massive force against the expedition's supply lines and forcibly drive it out of Mexico. Funston reacted by ordering Pershing to withdraw all his troops from San Antonio de Los Arenales to Colonia Dublán. Although the order was rescinded on the evening of May 11 when no evidence of Carrancista troop movements was found, the southernmost supply depots had been closed and materiel sent north that could not easily be turned around. Pershing was ordered to halt in place at Namiquipa, making tactical dispositions of his forces there and on El Valle to the north. The movements began a gradual withdrawal of the expedition to Dublán. On May 19 units of the 10th and 11th Cavalry returned to the base to guard the supply lines with Columbus and conduct reconnaissance in the absence of the temporarily grounded 1st Aero Squadron. As the threat of war with the de facto government increased, the northward movement continued. Pershing's headquarters left Namiquipa on June 21, setting up again in Dublán, after which the advanced supply depot at Namiquipa closed June 23. June 29 found the expedition concentrated on the main base and a forward camp at El Valle 60 miles to the south. The last and most costly engagement of the Mexican Expedition was fought on June 21 when 3 officers and 87 men of Troops C and K of the 10th Cavalry, sent separately to scout Carrancista dispositions