The plan was audacious. Confederate Brigadier General Henry Hopkins Sibley intended to sweep through New Mexico Territory, seize the gold and silver mines of Colorado, and push all the way to California. In February 1862, Sibley outmaneuvered Union Colonel Edward Canby at the Battle of Valverde, then bypassed Fort Craig and marched north up the Rio Grande Valley. By March 10, Confederate forces occupied Santa Fe. The invasion was the westernmost military operation of the entire Civil War, and the South's only serious attempt to conquer and occupy Union territory. All that stood between Sibley's Texans and Fort Union, the key federal outpost controlling access to the north, was a mountain pass on the old Santa Fe Trail called Glorieta.

Union forces under Colonel John P. Slough of the 1st Colorado Infantry performed a forced march from Denver, over Raton Pass, to Fort Union, and then on to Glorieta Pass, covering the distance in just 14 days. Major John M. Chivington led the advance guard. On March 26, Chivington's 418 soldiers surprised a Confederate picket of 50 men at the summit of the pass, then drove Major Charles Pyron's 300 Texans back through Apache Canyon in a running fight. Chivington flanked the Confederates repeatedly, catching them in crossfire and forcing retreat after retreat. The small victory at Apache Canyon was a morale boost, but reinforcements swelled both armies overnight. By March 28, roughly 1,300 Union troops faced over 1,100 Confederates, and both commanders decided to attack at dawn.

The main battle on March 28 was brutal. Slough sent Chivington on a flanking march while he engaged the Confederate front near Pigeon's Ranch. But Confederate Colonel William Read Scurry advanced faster than expected, and the two forces collided around 11:00 in the morning. Lieutenant Colonel Samuel Tappan's Colorado battalion held for half an hour before being outflanked. The fighting raged through the afternoon across adobe ranch buildings and ridgelines. Confederate Major John Shropshire was killed leading an attack on the Union left. Major Henry Raguet fell mortally wounded storming the right. From a ridge later called Sharpshooters Ridge, Confederate riflemen picked off Union artillerymen below. By late afternoon, Slough ordered a retreat, leaving the Confederates in possession of the field. On paper, it was a Confederate victory.

While the main battle raged, Chivington and his flanking force had found something far more valuable than an exposed enemy flank. They discovered the Confederate supply train at Johnson's Ranch, guarded by only a single cannon and a handful of men. Chivington's soldiers descended the steep canyon walls, overwhelmed the guards, and systematically destroyed everything. They burned 80 supply wagons, spiked the cannon, and killed or drove off roughly 500 horses and mules. Without supplies or transport, Scurry had no choice but to retreat to Santa Fe, and from there begin the long road back to San Antonio, Texas. A battlefield victory had been rendered meaningless by the loss of the supply train. The dream of a Confederate Southwest died in the smoke of those burning wagons.

In 1987, two Confederate burial sites were discovered at Pigeon's Ranch: the solitary grave of Major Shropshire and a mass grave of 30 Confederate soldiers. Shropshire's remains were reburied beside his parents in Bourbon County, Kentucky, in 1990. The other 30 were reinterred in Santa Fe National Cemetery. The Civil War Sites Advisory Commission gave Glorieta Pass its highest rating, Priority I (Class A), placing it alongside Gettysburg and Antietam as a principal strategic operation that directly impacted the course of the war. Only 10 other battlefields received the same distinction. Today, portions of the battlefield are preserved within Pecos National Historical Park, while roughly 80 percent remains in private hands. The pass itself is quiet now, a stretch of piñon and juniper in the Sangre de Cristos where the sounds of cannon and musket fire faded more than 160 years ago.