Here in the middle of NJ we don’t have anything we call a holler. I hear about them in songs but just how big would a holler be? Is it something you walk across in a few paces or is it a mile across? Is it round or long and narrow? Wikip says a stream bed or small valley but I’m not getting a size perspective from that. From an old bluegrass song I know you can chase a bear that’s making 90 miles an hour and taking 30 feet a jump through one but again, no size perspective. My 50’ x 150’ lot is on a block about 10 lots long, so about 300’ x 500’. Would that fit into a holler?
Ok, what you do is, you holler as loud as you can. The furthest distance you can be heard is referred to as a “holler”. 
A hollow is a creek is a stream. They’re all regional variations of the same thing: a small stream of fresh water*. Then were named before any standard definitions were set up and it was up to the local residents to determine what to call one, on the basis of “I know them when I see them.”
*Except in a few areas of Long Island and the UK, where a creek is a small tidal estuary.
A holler is a geographic feature, not a unit of measurement. Depending on where you are, a holler might be called a gulley, ravine, gulch, etc. It’s too deep and the sides too steep to cross on foot, not so big that you can’t make out what’s on the other side. When a holler starts to get really big, you’ll probably call it a valley.
Does that help?
As an Appalachian, I’ve heard alot people say holler, and never once has it been used to refer to a stream*. (Nor does my Mac’s dictionary list this usage.) A stream (or freshwater spring) often flows through a holler, but not necessarily.
Locally, holler is used in the sense of ‘small valley’, thus denoting the open space between two roughly parallel ridgelines or hillsides, usually heavily wooded, often containing a rudimentary roadbed for access. Picture traveling through a corridor shaped like a very slightly flatbottomed letter ‘V’. For linear distance I’d say between 100 and 1000 yards is average, with a peak-to-peak straightline measure of the ridgelines (the tops of the V) coming in around the half that range, and the bottom (the part that would contain the roadbed) offering between 5 and 100 yards of more or less level terrain, terminating, of course, at a rundown, mossgrown cabin, replete with a couple of redtick coondogs napping on the porch and a grizzled hillbilly lounging in a rocker, wearing denim overalls with one gallus unhooked, smoking a corncob pipe with a shotgun across his lap that will be brought to bear should you be a Revenuer. 
On Preview, Kunilou posted while I was typing, and in reply to her (him?) I’d say hollers (as I know them) are not impassable side to side, but doing so would strenuous-bear-crawling versus climbing.
*Local synonyms for stream, in descending order of prevalence, include-creek, stream, branch, run or possibly crick (limited to the oldtimers). Spring might be used if the origin of said stream is known and nearby (within a few hundred yards), but more often spring denotes the actual fountainhead of the water.
Not here in North Jersey either. I always thought that a hollow was some sort of cave. (As in, a hollowed-out piece of land)
Thanks for fighting my ignorance!