On the morning of March 3, 1946, a Douglas DC-3 departed Tucson heading west toward San Diego. It never arrived. Somewhere in the mountains east of San Diego, in terrain that aviators had been crossing with increasing regularity since the introduction of commercial air service, the aircraft struck Thing Mountain and killed everyone aboard. Twenty-seven people — three crew members, twenty-two adults, two infants — died in a crash that, at that moment, was the deadliest accident in American airline history. The wreckage sat undiscovered in the mountains for sixty-nine years.
American Airlines Flight 6-103 departed Tucson, Arizona at 5:59 in the morning on its final westbound leg to San Diego — the last segment of a transcontinental route originating in New York. The aircraft was a Douglas DC-3, the workhorse of postwar commercial aviation — reliable, widely flown, carrying passengers across routes that before the war had required trains.
Something went wrong in the mountains. Whether it was weather, navigation error, a mechanical problem, or some combination of factors that investigators could never fully reconstruct was in part a moot question — the aircraft was gone and no one knew exactly where. The search that followed covered the mountains east of San Diego without success. The aircraft simply did not turn up.
At the time of the crash, the death toll of 27 made American Airlines Flight 6-103 the deadliest commercial airline accident in United States history. The record did not hold long — commercial aviation in the postwar years was expanding rapidly, and with expansion came more accidents, some with higher death tolls. But in March 1946, this was the worst that had happened to American air passengers.
The passengers and crew represented the normal cross-section of postwar commercial travel: businesspeople, families, people moving through a country that was reconnecting after years of wartime disruption. Two of them were infants. None of them survived. The aircraft had been carrying the optimism of a returning normalcy — commercial air travel resuming and expanding after years of military priority — and the mountains took all of it.
The wreckage of Flight 6-103 was not found until 2015. For sixty-nine years, the aircraft lay on Thing Mountain in San Diego County's backcountry, in terrain that is rugged enough that even a systematic search failed to locate it in the weeks and months after the crash. The mountains east of San Diego — the Laguna Mountains, the In-Ko-Pah range, the Jacumba Mountains — are not impenetrable wilderness, but they are large, and aircraft debris in rough terrain can be invisible from any distance.
The discovery in 2015 closed a mystery that aviation historians had noted but largely accepted as unresolvable. The identities of the victims had been known from passenger manifests; the location of the aircraft had not been. Finding the wreck confirmed the crash site but could not answer the question that mattered most: why the aircraft was where it was.
Thing Mountain takes its name from a roadside attraction that operated on the old Highway 80 below — a tourist stop called simply 'The Thing,' which drew travelers curious about its ambiguous exhibits. The mountain itself is unremarkable in the sense that all mountains in this part of San Diego County are remarkable: granite, rugged, rising from chaparral country into elevations where the terrain becomes genuinely challenging for anyone on foot.
For pilots crossing these mountains, the challenge is the terrain's height relative to the cruising altitudes of aircraft at the time — the summits in this range reach high enough that even a few hundred feet of error in navigation or altitude could prove fatal. The DC-3 that struck Thing Mountain on March 3, 1946, encountered this reality at 5:59 in the morning. The mountain is unchanged. The old highway below it is now mostly superseded by Interstate 8. The 'Thing' roadside attraction still operates.
Thing Mountain, where American Airlines Flight 6-103 crashed, is located at approximately 32.828°N, 116.527°W in the Laguna Mountains of San Diego County. The mountain terrain east of El Cajon — the Laguna Mountains grade along Interstate 8 — represents the challenging airspace context for this accident. Nearest airports: KSAN (San Diego International, ~35 nm W), KSEE (Gillespie Field, ~25 nm NW), L78 (Jacumba, ~15 nm SE).