"Locomotive" was written by Miranda and Ashley, with K.S Rhodes (a Tennessee artist who has worked with Ashley before). I think some of the references in it do draw on personal feelings.
I think Napa Valley is being used to symbolize wine, though, rather than being a place to visit. This is the verse in question:
"I ain't no Napa Valley,
New York City seems okay
>I'm a little bit more Tennessee
and there's whiskey in my veins"
The contrast between wine and whiskey is a quite common theme in Country Music (Carrie herself used it in "Wine After Whiskey", which I think is one of her best "lost love" songs). Whiskey is seen as not only stronger, but also as more down to earth, less sophisticated, and therefore more tied into the Country ethos. A contrast between California (and its presumed life style) and the Country Music "heartland" is also quite a common theme (the Dixie Chicks, for example, throw a dig at the California life style image in their pre-album release song). Something similar may be meant here. Miranda has often appeared to have a closer relationship with New York. Her team pitched her to the New York media early on, when they were having some difficulty in getting Country radio to warm to her, and the New York press has usually tended to give her good reviews. I think she has a flat there, and feels a connection with the town (for example, being photographed with the "protect yo heart" street grafitti). Her husband, Brendan, is from New York. California, though, may have less happy connotations for her. Her first marriage may have floundered, at least partly, after Blake Shelton made his base there, and seldom appeared to come home. Our late friend, Windmills, believed that many of the "sources" quoted in the tabloid attacks on her came from people connected with the TV franchise, who saw an alleged feud as good publicity for the fans of her ex-husband's show.,
I like "Locomotive". The music is acknowledged to have Punk influences - and as an old fan of the Cowpunk band, Lone Justice, that pleases me!
This is a live performance of Locomotive:
https://www.youtube.com/watch?v=XSnFpSoKsdA
And, for comparison, one of Lone Justice's best known songs:
https://www.youtube.com/watch?v=nNf-1DJCrPc
I know Maria was considerably younger then than Miranda is now, and we can't expect the spirit of those days to be just re-created today - but I like to think there may be a touch of homage in the way the music was conceived
In fact, I think she left a musical legacy that probably was an influence on many young girls growing up, who both wanted to be Country singers, and wanted their take on Country Music to be forward looking. For example, this is Carrie's cover - from her 2001 indie album "Carrie Underwood" - of a very differently styled Maria McKee song:
https://www.youtube.com/watch?v=HnDZo4Fmy_A