These were former passenger or dual service units running out their last miles on freights. They were concentrated mainly in Texas and were maintained at Cleburne Shops. They were more common on branchline trains, but there are photos of them coupled to Alligator RSD-15's still in transcontinental mainline service. They could turn up anywhere including the west coast.
They used both yellow warbonnets and the 7 blue warbonnet F-7A units in all types of freight service, often in Texas and Oklahoma, and also in seasonal grain service as far north as Superior, at the top of the grain funnel, as reported in RailClassics 1978 Yearbook. Amtrak did not like the yellow warbonnet paint scheme, though two of the 15 yellow warbonnet A units did operate in Amtrak service briefly.
There is no record of a bluebonnet ever operating in Amtrak service.
I have a friends photo of a Bluebonnet F7 on the Dallas Branch. It looks like it was just painted in the photo, so it may be a first run.
Did the Santa Fe use their F7 in their Bluebonnet scheme in branch line service? Or did they continue their main line operations?
Amtrak America, 1971-Present.