On Cuesta that could have just been head end helpers. That's not the "optimal" power distribution that has become the "thing" it is today, but back then I ran quite a few head end helps, more often eastbound, out of Colton, but once or twice out of thousand Palms when the rear helpers didn't have what it took. And, once when a train stalled out above Hugo.

Way back when they were using GP-9's as helpers, you'd go out to Myoma with two geeps, and push from the behind the caboose up the grade to Beaumont. Higher horse power units used as helpers, able to push lighter bay window cabooses, right of off the rails put an end to that.

Or it may have just been moving power to where it is needed. I once had a cab-hop with 8 road units from Indio to Yuma. All of that weight of units really gooses the mileage rate, and it was a great trip, really fast, since you don't have to drag that pesky 7000 feet and 7000 tons or so of train around.