There a lot of possible answers for this question. As shown in the image, we can infer one of the following characteristics that could be used to determine if an intrusive igneous rock has a mafic composition:
<span>- color/light color/dark color - density/low density/high density - mineral composition - rich in Al, Si, or rich in Fe, Mg - presence/absence of quartz/potassium feldspar/pyroxene/olivine</span>
You're right that volcanoes are out. We can find each of the abovementioned landforms in the USA, but about 50% of them are plains. They're specific for central USA and southern coast.
