Capitalization

Q. “Bigger than whole states in America’s lower 48.” CMOS seems to advise lowercasing lower, but it’s also a common phrase and almost looks like, if spelled out, it should be italicized or capitalized—or both. I could use your help. Thanks.

A. Merriam-Webster’s 11th Collegiate Dictionary styles it “Lower 48,” and in the absence of advice in CMOS, we follow M-W.