Utah! Who knew? My first reaction to the black squares was that they looked like quotation marks, and I thought that might be a cute theme. Cece and I did this together. We got into the gird with the little section of 3-letter answers in the NW: STS, MIA, ENT, which lead Cece to get BEATSME, and me to get INLATIN. Nothing else was immediately apparent to us there, so we moved to the middle.
Cece immediately, without any crosses, suggested CONESTOGA. Wow. OAS followed, and ATMS (good clue there), and then ASSISTED and STMARYS (a guess, that).
So then we got the theme with UTAHSTATE, which led to the 2 15-letter answers, TABERNACLECHOIR and LATTERDAYSAINTS.
The corners, once again, were nice and chunky. Some answers I did not like: REPEALS, for the clue (The 21st Amendment and such) - why not make it the verb instead? As a noun it feels super awkward. ISOTONE is a real thing, but not something I knew. I went for ISOTOpE, which is actually two atoms that have the same number of protons but a different number of neutrons, so the exact opposite. And that was my error in the puzzle. DEME is a desperate piece of fill. I don't like the definition of TWEEDLE, even though I feel I've seen it before in the NYT puzzle.
BIGMAC is a nice piece of trivia. I wanted "Reuben" first, but that sandwich was invented in the 1920s. PEACHPIT is a fine answer. MAINE is definitely a "Big source of blueberries," and I always think of "Blueberries For Sal," a delightful book. 43A: Things you might enjoy with your best buds? (IPODS) is cute. 37D: One way to be held (HOSTAGE) was a shocker (not a SHANKAR).
Other answers Cece got: GRABSAT, STINKAT. We both had a strangely difficult time getting HORSE (23A: Mount), even with HOR__ in place.
So, TILSIT, IONBEAM, and ISOTONE. That made the SW the most difficult corner, and our stumbling block.
Mostly a thumbs up from me.