How about the region where I live and been to - Pacific Northwest - it could be based in Washington, Oregon, Idaho, and up to British Columbia in Canada.
Lots of variation in terrain The major cities (Vancouver VC, Seattle, and Portland) and lots of smaller cities along the way perfect for various gym cities. We also have the Cascades range in the middle of Washington and Oregon with various dormant volcanoes and tall mountains, ocean on the west coast, plains on the eastern side, vast forest, lots of rivers. Hot summers, and unexpected rains, heavy snowfall on the mountains and volcanos.