There is actual volcanic debris along I-40 in the interior of California also. I saw it myself.
If you are talking about my statement about the center of North America, I was not talking about the interior of California, or the Yellowstone Caldera. Having spent time in Iowa, my concept of center of North America is from around there and northward. Yellowstone Caldera is in the Rocky Mountains which is entirely different from the center of our country and Canada which in eons past was a great shallow inland sea, not home to volcanic activity. Also, I am very aware of Yellowstone as my father wrote a fiction book about a major eruption of Yellowstone in our own times.