For as long as I can remember, people in southern California have referred to “The Valley” with equal parts horror, disgust, contempt, and distaste. As someone who has never been to California, I have two questions:
Maps of California show many valleys. Exactly which valley is this infamous one?
Why does every one have such a negative reaction to the place?
Uber suburbia.
The San Fernando Valley is probably the one you are referring to. It is the part of Los Angeles between the Santa Monica Mountains and the San Gabriel Mountains if my memory serves me correctly. It is where “Valley Girls” and such come from. It is not to be confused with The Central Valley, which is between the Coastal Range and the Sierra Nevada Range and among the best agricultural land in the world, having very long ago been the subject of the TV series The Big Valley starring Miss Barbara Stanwyck, Lee Majors and Linda Evans. http://www.imdb.com/title/tt0058791/
Totally!
Also The Porn Capital of the world. Poor air quality, crappy traffic, generally a giant shit-hole.
I had the misfortune to live there a couple of months. A real low-point.
To the max!
San Fernando Valley is home to places like Van Nuys.
*2. Why does every one have such a negative reaction to the place? *
As John Mace suggests, for some people it represents the worst aspects of suburbia.
On the other hand, some areas in The Valley are more on the rural side and even some of the fully suburban neighborhoods are very nice.
Look at the satellite view of the San Fernando Valley on Google maps and as you zoom in, you’ll see that in some areas, you can’t see the houses for the trees and in other neighborhoods, suburban blight rules the landscape. So it really sort of depends on where you go.
That video makes the town look far more glamorous than it actually is. 
Several years back, there was an initiative on the ballot for the S.F.V. to break away from Los Angeles and create its own city. The thing I remember most is that if it had succeeded, S.F.V. (or whatever name they chose to call it, one of the ballot options was “Camelot”) would’ve become the largest city in America without a single museum.
Like, what-everrr
That would be the San Joaquin Valley
That isn’t entirely true, of course, but I’m pretty sure all of the “big” museums are elsewhere.
I’m amused at the thought that Van Nuys (where I live) would be considered suburban. It’s not my idea of suburbia.
Re: Museums in The Valley–If Sylmar counts as being in the valley, The Nethercutt Collection is an excellent museum.
Shout out to the SGV! My hometown is there! The other big valley in LA…San Gabriel. 
Beat me to it! I was just going to pop in with this. (Is there some reason Sylmar would not count as Valley?) Collection of classic cars and antique mechanical music-making machines. (If you’re into classic car collections, and you’re in Los Angeles, there’s also the Petersen Museum a block or two from the La Brea Tar Pits.)
I grew up in Pacoima/Arleta area, c. 1950’s-1960’s. The Valley was rather fully built-up even then, but there were still some not-quite-fully-cement-jungle areas remaining here and there, especially around the edges. It’s way more fully built up now. The air quality then was vastly worse, because that was before there was much of environmental regulation. With the air quality and smog rules now, it’s much better. Still pretty bad.
In the neighborhood where I lived, we didn’t feel the need to keep the door locked by day, but we locked up at night. Today, in that same 'hood, you wouldn’t walk outdoors without your Uzi.
Once upon a time, in the dimly-remembered past, this area was the “outlying” agricultural land, with citrus groves, avocado, other orchards and cropland and ranches. Even in the 1960’s, in the middle of things, there was an orange grove at the end of my block, right in a suburban subdivision. Looooong gone now! Today, you can still find some of that in the next valleys to the north and northwest, Conejo Valley, Ventura area, and Simi Valley.
As noted already, NOT to be confused with San Joaquin Valley, the huge largely agricultural area stretching from Bakersfield northward to Sacramento and beyond, along I-5 and State Route 99.
Are you considering a visit to the Golden State? (All the gold of which, of course, is in a bank in the middle of Beverly Hills in somebody else’s name.)
No, the Central Valley comprises both the San Joaquin Valley and the comparably large Sacramento Valley, plus, arguably, some other little bits too. The Central Valley is a very distinct and cohesive geographical feature,* but it consists of (at least) two quite separate watersheds.
As others have said, however, “The Valley”, at least for people in the Los Angeles area, means the San Fernando Valley. And those who do not actually live there tend to be a bit snobbly about it. It is not actually all that bad, if compared with other parts of L.A. suburbia, but it is the place of origin of the notorious Valley Girl language.
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*If you look at a relief map of the entire USA, it is about the most obvious and noticeable feature there is.
My thanks to the OP because I’ve never really understood the “Valley Girl” references. I thought it was a generic name for scatty snobbish high school girls from LA.
I’ve spent time in the San Joachim Valley which is verdant and interesting.
[nitpick]
Hmm, if we are trying to avoid confusion, I would say that Sacramento and points north are not in the San Joaquin Valley.
I spent a fair amount of time in the Central Valley (first mentioned in this thread in The Second Stone’s post #3, with an accurate description IMHO), and would say that the various Wikpedia articles are spot-on geographically, namely that the Central Valley contains the San Joaquin Valley to the south of the Sacramento–San Joaquin River Delta, and the Sacramento Valley to the north of the delta. [There is also the Tulare Basin, but that is much smaller and less significant than the other two parts.]
You and drachillix (post 11) seem to want to refer to the entire Central Valley as the San Joaquin Valley, and I am reasonably confident that Central Valley residents north of the San Joaquin County / Sacramento County line (including Sacramento, Davis, Chico, etc) would disagree.
[/nitpick]
Of course none of the above (as we all agree) are the OP’s “The Valley”.