The quote that best represents Regionalism in "The Celebrated Jumping Frog of Calaveras County" is:
"So he set there a good while thinking and thinking to hisself, and then he got the frog out and prized his mouth open and took a tea-spoon and filled him full of quail shot. . ."
This quote highlights regional dialect, local customs, and a focus on the specific setting and characters typical of Regionalism, capturing the unique flavor of the local culture in Calaveras County.