I haven't seen Shasta in other literature or name indexes for individuals, but Mount Shasta and Shasta county are named for the Shasta people (today the Shasta Indian Nation), a California tribe that has been very close to extinction more than once. I'm doubtful that Lewis would have been aware of them, unless he somehow came into contact with someone from the nation. It would be cool if he did, though!

I would also note that Shasta is very close to the Persian/Pashto name Shaista (Shayesteh), meaning worthy of admiration. I've only ever heard/seen this name for women, but given that Aravis is Greek for "Arab" and Lewis pulled a lot of generic Middle Eastern tropes for his design of Calormen, I wouldn't be surprised if it might have been an influencer.

@wren Thank you! The Persian etymology definitely makes a lot more sense; even if Lewis did know about the Shasta people and/or one or more of the geographic features named for them, there's no clear reason why he would have chosen to use the name as a Calormene name, whereas a Persion word would seem much more likely. Thanks again!

I wouldn't be surprised if C. S. Lewis didn't think that much about the etymology of the name and just liked how "Shasta" sounded-or maybe he disliked it since Aravis says that Cor is a nicer name.