Definitely not ONT, the mountains look too close and the old Tower would have been visible in the background not long after they got airborne.
Well, I am 99% sure it's PSP. After taking a quick look at Google StreetView around PSP, the mountains match up. This AA DC10 would likely be a 125pm to PHX, taking off toward the southeast. Keep in mind, it didn't take up much runway.
I re-watched the video and looked at GSV images of PSP and I'll take your 99% and raise you that it is 100% PSP.
I made a mistake on my first watching and thought that the low cloud cover was a body of water but in re-watching the mountains are a total giveaway.
Thanks everyone, nice investigative work! While I kept thinking outside the box (including YVR, GEG, RNO, etc), PSP never occurred to me. But AOGs from the time period indeed show AA DC-10 PSP-PHX segments during the winter, then 722s at other times of the year.
Interesting all the clouds in the video which may be a winter system about to affect normally sunny PSP (which is leeward or on the drier side of mountains). Such systems give a normally dry Palm Springs occasional winter rains (and very rare snows even at low elevation).