The Union and Confederate forces met at the Battle of Glorieta Pass on March 28. The Confederates were able to push the Union force through the pass, but had to retreat following the destruction of their wagon train, which contained nearly all of their supplies and ammunition. Sibley pulled his army back to Albuquerque to await reinforcements from Texas. Slough, receiving orders from Canby to return immediately to Fort Union, also retreated, fearing a court martial if he disobeyed this order. Once he arrived at the fort, he resigned his commission and returned to Colorado, leaving Lieutenant Colonel Samuel Tappan in command of the regiment and Paul once again in command of the fort.