o10, I'll guess not everyone here enjoyed your "Detroit" tale as much as I did. I grew up in MI but didn't visit Motor City often until I was in college. Then the love of jazz drew me in.
I don't remember the 20 Grand, but Detroit had a number of small bars/clubs which we called organ bars. That was because so many of them had something like the Hammond B3 in residence and there were enough local musicians to play them, in addition to occasional name jazz musicians. Baker's Keyboard Lounge is the only one I now remember.
But my favorite was the Minor Key. The name was a double entendre with the reference to music as well as not having a liquor license. They consistently brought in major stars and I heard Miles, Coltrane, Cannonball, Silver, The Jazz Messengers, Getz, etc. there. One advantage was it was a small club so no seat was far from the stage.
The Minor Key was located in the heart of black Detroit (as I recall, Dexter & Burlingame near where the riots broke out in 1967 which destroyed the club). The first set would begin around 9 PM and up to half of the audience would be white students from area colleges. The second set would see that reduced to about 20-25% white. By the third set, usually after midnight, we would be the only non-blacks in the audience. There was never any problem. I guess we were accepted because we obviously cared about the music to be there at that time.
In fact, because of the small size of the room patrons often ended up sharing tables. The club only offered soft drinks or "set ups" and a little food. Many times our table companions would offer to share their flask, something they all seemed to bring. Being underage that was fine with us.
The Detroit of today is far different. But I have friends there and also reading articles I've learned there is a resurgence movement, at least in the central area. How much of that continues the great jazz heritage of the city I can't say.
BTW, she lived in Pontiac but drove a Buick? ;^)