Please read:
I upload these photos of what I think may be a Spizella pusilla, specially based on the pink color of the feet, as the Pyle says that's a way to tell them apart from the Worthen Sparrow. I´m not sure if the ID is correct and for that, I ask the ebird regional reviewer for help. I provide additional information for discussion below. (The photos were taken on Worthens territory)
There are 4 main differences between the Spizella pusilla and the Spizella wortheni according to the IGNAB by Pyle, these characteristics are the following:
1). The brownish crown of the s.pusilla extends to the bill (nevertheless on Merlin and Birds of the World there are photos of s.pusilla having a brownish crown separated by a gray forecrown, more similar to the wortheni)
2). The s.pusilla has a distinct white wing bars: However, the subspecies of s.pusilla that distribute in winter in Northern Mexico (s.pusilla arenacea) has duller plumage, maybe that can affect also the white wing bars, but not sure.
3). Chest usually washed brownish vs the grayish chest on the wortheni: This is a characteristic that I can't really see in the individual taken by me on photo.
4). Legs flesh pink: That's one of the main reasons why I think this individual may be a Spizella pusilla, in the pictures and in the field I could see the pink leg flesh.