Wikimedia has a decent SVG US base map. I’ve seen this exact map used on news broadcasts. It’s a clean design, has crisp state borders, and is great starting point for customization:
One customization you could try is adding US National Parks. I followed this tutorial to create this map:
Once you have the geographic data in a compatible format for the map projection you’re using, you can do things like copy a set of SVG elements using a text editor and create a new map with that extracted data. You can scale SVG maps to any degree you’d like (try zooming in/out on these) without degrading the resolution.
Here is an example of Yellowstone National Park and surrounding state data extracted from the above map. I added a thin black border around the park boundary:
A similar extract for Shenandoah National Park and Virginia: