Andrew Beahrs makes the case:
Twain didn’t just want mussels; he wanted steamed mussels, from San Francisco. He wanted terrapin from Philadelphia, stewed with sherry and cream (the recipe’s main rival, from Baltimore, omitted the cream—Twain loved cream). He wanted partridge from Missouri, shad from the Connecticut River, and perch and canvasback ducks from Baltimore. The list went on. These were things that depended on the grasslands, woods, and waters of especially American places. And they were things that, in Twain’s youth, could be found nowhere else.
Beahrs is author of Twain’s Feast: Searching for America’s Lost Foods in the Footsteps of Samuel Clemens, which I have just purchased on Amazon.
Show Me Eats 
“local” was more or less the default in Twain’s time, and there was no shame in preferring better food from better sources. It’s a more recent phenomenon to cast food as a lowest-common-denominator commodity that we’re not supposed to have opinions about.
You might enjoy this post of ours from fall 2008, on Twain-as-locavore:
Twain was far, far ahead of his time on religion, colonialism, and lots of other stuff. The more I learn about him, the more I want to name my first born after him.
Steve, you guys need to get working on that. And are you going to go with “Langhorn” or “Clemons?”