When I later learned that the flag was associated with a more libertarian worldview than a careful-outdoor-recreation sentiment, I had assumed that it was a relatively recent invention. It turns out the flag actually dates back to the American revolution. There's some interesting history in Wikipedia's First Navy Jack article and some less-well-cited information on the Gadsden flag article. The latter has this interesting tidbit:
As the American colonies came to identify more with their own communities and the concept of liberty, rather than as vassals of the British empire, icons that were unique to the Americas became increasingly popular. The rattlesnake, like the bald eagle and American Indian, came to symbolize American ideals and society. … Benjamin Franklin published an essay in the Pennsylvania Journal under the pseudonym American Guesser in which he suggested that the rattlesnake was a good symbol for the American spirit: I recollected that her eye excelled in brightness, that of any other animal, and that she has no eye-lids—She may therefore be esteemed an emblem of vigilance.—She never begins an attack, nor, when once engaged, ever surrenders: She is therefore an emblem of magnanimity and true courage.—As if anxious to prevent all pretensions of quarreling with her, the weapons with which nature has furnished her, she conceals in the roof of her mouth, so that, to those who are unacquainted with her, she appears to be a most defenseless animal; and even when those weapons are shown and extended for her defense, they appear weak and contemptible; but their wounds however small, are decisive and fatal:—Conscious of this, she never wounds till she has generously given notice, even to her enemy, and cautioned him against the danger of stepping on her.—Was I wrong, Sir, in thinking this a strong picture of the temper and conduct of America?
This leads me to imagine a mashup flag of Ben Franklin's choices national mascots, the turkey and the rattlesnake, perched on a cactus à la the Mexican coat of arms. I'm also reminded of a Gadsden flag parody a friend told me about with an ouroboros on a yellow background with muffled words at the bottom. I regret that I have not been able to find this via Google Image Search.
Wikipedia also notes
As the American Revolution grew, the snake began to see more use as a symbol of the colonies. In 1774, Paul Revere added Franklin's iconic cartoon to the nameplate of his paper, the Massachusetts Spy, depicted there as fighting a British dragon.The rattlesnake as a characteristic American dragon is an interesting idea to play with, particularly as an ally of the people (like an east Asian dragon) rather than as a foe to be conquered (like a typical European dragon).
The snake may also be an interesting symbolic way to segment the American right wing. The liberty and independence faction celebrates the rattlesnake as a mascot. The Christian traditionalist faction distrusts snakes generally, due to their association with temptation in the Garden of Eden.
I'm also glad to see that empowered women have thought of not treading on Medusa and put it on shirts and tote bags.