By December of 1846, the United States had steered the fate of the Mexican-American War into the sooted streets of El Pueblo de Los Angeles. After over half a year of combat, a revamped campaign to recapture Los Angeles from the Californios was devised by two brash military commanders. The decisive strategy would secure Alta California and wrench a surrender from Mexican authority. After the war was won, sights were set on mapping the economic possibilities of the uncharted San Gabriel Mountains.
One of the Last Lines of Defense: San Gabriel River
Underestimating the defiant spirit of the Californios at the Battle of San Pasqual a month before, the wounded American General Stephen W. Kearny, under the overall command of Commodore Robert F. Stockton, amassed an overwhelming military response to overtake Los Angeles. On December 29, 1846, the Stockton-Kearney force, a well trained six-hundred-man expedition of sailors, marines, and dragoons, heaved north out of San Diego. Mexican Governor-General José Flores, desperate to avoid engaging in combat with his bedraggled crew, dispatched a last ditch attempt in the form of a cease-fire proposal on New Year's Day. Stockton vehemently refused to lay down arms, and rapidly advanced his men towards Los Angeles -- now heading west through the San Gabriel Valley, not far from the ruins of Mission San Gabriel Arcángel.
Stripped of any recourse, Flores was forced to fight. In the face of the staggering might of the American campaign, he shoved together roughly 450 poorly armed and heavily dispirited soldiers, four pieces of artillery, and what remnants of gunpowder he could muster. With his wanting troops, Flores decided to focus on taking advantage of Stockton's blaring vulnerability: the unavoidable river crossings that the Americans would have to breach en route to Los Angeles. On January 7th, Flores positioned two nine-pounder cannons, sharpshooters, mounted lancers, and horsemen squadrons on a fifty-foot-high bluff above a ford of the San Gabriel River. In his "Notes of a Military Reconnoissance," American Lieutenant W. H. Emory recorded what was encountered the next day:
We passed over a country destitute of wood and water, undulating and gently dipping towards the ocean, which was in view. About two o'clock we came in sights of the San Gabriel river. Small squads of horsemen began to show themselves on either flank, and it became quite apparent the enemy intended to dispute our passage of the river.
The Americans marched through the knee-deep river under musket and cannon fire by the Californios, but lost momentum as their boots and artillery were sucked into the quicksand bed of the hundred yard crossing. Easy targets in sight, Flores was handed an advantage. Yet the Californios' low-grade powder and poor aim proved a weak assail on Stockton's men, inflicting few casualties. Inspired, Stockton rallied his struggling troops, personally charging into the water to rescue one of his sinking cannons and shouted: "Quicksand be damned, come on boys!"
While Stockton pounded the Californio's bluff with cannon shot, Kearny's party of bayonets clamored up the hill. Flanked by Flores' horsemen near the bluff's summit, the American general drew his men into a square formation and drove off the cavalry. Lieutenant Emory recalled the victory: "the 1st battalion...was directed to rush for the hill, supposing that would be the contested point, but great was our surprise to find it abandoned." It took only ninety minutes to repulse Flores and his men from the bluff.
After the Battle of Río San Gabriel, American victory would be swift. On January 10, U.S. forces retook Los Angeles. Three days later, the Californios would officially surrender upon the signing of the Treaty of Cahuenga on January 13, 1847.
Mapping the Sierra Madre
By the time the U.S annexed Alta California from Mexico in 1848, economic interest in the little-known mountains above the new American town of Los Angeles was growing. The San Gabriel Mountain Range had never been officially mapped and surveyed until 1853, when Congress appropriated $150,000 for surveys to find a practical and economical route for a transcontinental railroad. The newly formed Army Corps of Topographical Engineers directed the Pacific Railroad Survey to scout six possible cross-country railroad routes.
Under the guidance of Lieutenant Robert Stockton Williamson, the party journeyed into the San Gabriels to scout a route from San Francisco that would make a connection with a 32nd parallel transcontinental route. Williamson recommended a route through a pass in the western flank of the mountains that would eventually be used by the Southern Pacific in 1875. Mount Williamson was named in honor of the man that led the first government expedition into the transverse range.
In January 1861, a young man named William H. Brewer made his way toward the San Gabriels to take barometrical observations for a new mapping party called the California Geological Survey. In "Up and Down California in 1860-1864," Brewer recalls his first foray into the range:
It was the steepest and hardest climb I have ever had by far....The view was magnificent. All the lower hills to the west sank into the plain...and we could see a great distance, probably fifty or sixty miles, out to sea. Los Angeles, with its vineyards and all, was a mere speck on the landscape.
It was from an 1865 report issued by Brewer and Josiah Whitney's California Geological Survey that the mountains were given the name of San Gabriel, after its principal canyon that contained the headwaters of the San Gabriel River. They would continue to be known informally as the Sierra Madre.
Ten years after the report, a more thorough survey of the range was conducted by Lieutenant C.W. Whipple of the Wheeler Survey. Although he mistakenly identified a prominent peak as the highest in the range -- this false apex is still saddled with the name Mt. Disappointment -- Whipple managed to create the first detailed map of the once unknown mountains. The names that the Wheeler Survey affixed to many individual mountains, like San Gabriel and Cucamonga Peak, are still the official titles today. One hundred and fifty years later, these peaks continue to draw people armed with a map and a desire to explore.