What was the main tectonic setting of the western U.S. in early Paleozoic time?

A) continental collision
B) transform fault
C) passive margin
D) the interior of a supercontinent

During the early Paleozoic era, the western margin of what is now the United States was characterized by a passive margin setting. This means it was a relatively quiet and stable boundary without significant tectonic activity, such as the collision of landmasses or the presence of major fault lines. It was the edge of the continent facing the open ocean, with sedimentation occurring along the continental shelf and slope.