I must have been thinking about the Columbia River basalts. I did enough thin sections of those in undergrad petrology. Here we go,the following was copied from the USGS website.
An additional difference between Yellowstone and Columbia River/Newberry (CR/N) is that Yellowstone's magma is rhyolitic and CR/N's magma is basaltic. Rhyolitic magma is a lot more explosive than basalt, and indeed Yellowstone's eruptions have been among the most powerful observed in the geologic record. (The Huckleberry Ridge tuff, which erupted from Yellowstone 2.1 Ma, is deposited over something like half of the Lower 48!) CR/N, on the other hand, appear to be gentler eruptions more like Hawaii's oozing of basalt. I suppose this too can be explained by Derek's model: partial melting of the more-felsic crust under Yellowstone (as hot plume magma heats that thicker slab of continental crust), but a shallower Moho to the west, producing mafic magma a shorter vertical distance from the surface.