What cool specificity!
I saw a really cool sign on the private dirt road leading down into a valley that read, “Ain’t nothing in this holler worth dying over”. So much more color than just “No Trespassing”.
A hollow is like a valley in that it is surrounded by hills or mountains. However, it is so much smaller that they are totally different in what it means to be from one. Valleys are where the best farmland is and where the cities are. A hollow is still within the mountains and the soil is much worse and much more difficult to farm. So the implications of living in a hollow is that you are poor because the soil is so bad and isolated because you are surrounded by mountains. For the most part hollers refers to people from Appalachia and they are so isolated that their speechstill has words and phrases common in Elizabethan England from 400 years ago.
Due to television, a lot of that language is dying. The older people still use some of those phrases, but the younger generations don’t (and honestly at this point, by younger, I mean anyone under 70.) A few still hold on.
One anecdote that I use and is in that article is ‘I don’t care’ in reference to a question. In my dialect, ‘I don’t care’ is a polite way of saying yes. So for instance, if someone says ‘Do you want to go to the movies?’ If you say ‘I don’t care.’ it means ‘Yes, I would, but if you have something you’d rather do, we don’t have to go.’ In my extended family’s Chicago dialect, ‘I don’t care.’ is an emphatic no. I can remember as a young child staying with my aunt and uncle and they would keep asking me to do things and I would say ‘I don’t care.’ meaning ‘Yes’ and then they’d present another option and I’d get confused and say ‘I don’t care’ again until they got extremely angry and began screaming at me that I didn’t want to do anything and I broke down in tears not knowing what the heck they were talking about. I can remember saying, “I kept saying ‘I don’t care.’ Why are you so mad?”
What kind of holler? Are you sure he didn’t say “f****** holler” ? And smile when you speak of them — my ancestors were born and raised in some of those hollows. 
The high-rated TV series Justified will introduce you to the hollows of Harlan County. (And that lets me segue into mention of Pete Seeger’s support for Harlan County miners).
I read the piece that the OP is referring to. It was a distressing article in Rolling Stone, and the big-shot actor is Johnny Depp.
I was surprised to learn that he came from Kentucky, as I don’t remember ever hearing him speak with an accent.
My wife’s family is from Harlan County. I’ve visited - and yeah, a holler is so much smaller than a valley. The video that senoy linked is pretty accurate (though they’d argue that a holler would be even smaller, and perpendicular to that featured road leading up to just a handful of houses before the mountain gets too steep).
No mention yet of the residents of Hootin’ Holler?
WikiAppalachian English.
There’s an orchard/store/restaurant in SE Wisconsin called “Apple Holler”, but the land is flat that part of the state. 
Much of that reads like a parody of the dialect to me.
(Born and raised in Appalachia, though not in a holler.)
There’s no such thing as Appalachian English. It’s a related set of dialects, so what that is is a conglomeration of terms and grammar from various dialects that they smooshed together and called the same thing. Some of what they say is very familiar to me and some of it is absolutely gibberish. My guess is that if I were in North Carolina or Kentucky or Tennessee hill country, they would find those parts I find to be gibberish to be normal and the parts that I find normal they would find gibberish.
I know that even within my own state, my county has a dialect that is different than people one county to the south and it’s incredibly different than people from the southern part of the state. I live in Morgantown now and the accent here is practically a mellow Pittsburgh accent, but I grew up 60 miles away and it’s what I call a Highland accent.
I’ve always considered a hollow to be the watershed of a creek that runs down a mountain or hill. It’s a valley of sorts, but since it’s running down a mountain there is less arable land; the only good place for a road is usually along the creek and building sites require site prep to have enough level land or a usable road to the site, especially as one goes farther back up the hollow.
No, rich people live on the top side of hills (or in town). Down in the valley is where their farmland is (and their farmhands). Because the land down there grows better crops, and keeps them rich.
If they were born in a valley, then they were probably poor at the time. They became rich during their life, and ‘moved on up’.
The billy element of hillbilly comes from the old Scottish/Northern English billy/billie meaning fellow. Here’s OED:
On my property is Holler Branch. It’s part of a bigger water system called Holler Bayou. It runs into Holler Creek, a mile or so away from our land. And then there is the Holler relief. When the bayou floods it overflows into the Holler relief.
Holler Branch is a high sided cut with clear water running, or babbling over a gravel bottom. Crawdads are king in the branch.
ETA Holler doesn’t mean anything here. Just a name.
According to my Appalachian in-laws, a “holler” (those that are good spellers render it in print as “hollow”) is a small valley/dent between mountain tops. Saying someone was “born in a holler” basically is calling them a hillbilly (though for many the polite/PC term is now “mountain people”). Depending on context, it can also also carry a connotation of backwoods, backward, dirt-poor, ignorant, and bigoted. A lot depends on the delivery.
Other words ending in “-ow” might also be spoken with an “-er” ending, such as “winder” for “window” (example: “This darn Winders 10 on my computer is updating again!”). As noted, there isn’t really just one Appalachian English, it’s a group of related and neighboring dialects with a lot of little variation.
soma youin’s just r speaking like yawls gotta a chaw fulla cat heads
If’n ya doezn’t know yer holler from yer gully or’n yer swale you guys just aughtta keep yins dang pie eater from a’flappin’ in there here thread.
That is the definition I was going to give, luckily I read the complete thread.
For reference I grew up in the coal mining area of SW Virginia.
Yeah, I’m sure that they’re trying for a “down home / rural” feel with the name, but “holler” really is a Southern / Appalachian term, and even if parts of Wisconsin have areas that would qualify as “hollers,” I’m pretty sure that they aren’t called that.