(words and phrases which are used by locals, but which outsiders or newcomers may not understand)
Let me start with this: below is what I consider to be the typical Coloradoan's "mental map" of their state:
Only selected cities are labeled, based on the text that follows.
Following are more in-depth thoughts on what most Coloradoans mean by these (and other) terms. (By the way, if you're looking for pronunciations and meanings of specific places in Colorado, try my Colorado toponymy page.)
The Front Range
Where exactly is the Front Range? Most maps of Colorado don't label a certain chain of mountains "Front Range". That's because the term is loosely applied to any of the first mountains one encounters when heading west into the Rockies, from anywhere in the northern half of Colorado. Author Gleaves Whitney claims the term "Front Range" actually encompasses nine distinct, named mountain ranges (shown in purple on the map). However, when Coloradoans say "Front Range", they're not always referring to the mountains themselves. Often, what they mean is the heavily populated, flatter piedmont area that lies at the eastern foot of the mountains. Today the Front Range urban area (shown in gray on the map) is characterized by a nearly unbroken 140-mile-long string of cities and communities, anchored on the north by Fort Collins, Colorado Springs on the south, and bulging in the middle with the Denver metro area.
The Mountains; the High Country
Most Coloradoans don't pay a lot of attention to the specific names of mountains or mountain ranges. It's quite ironic: if you say "Front Range", everybody knows what you mean - even though they couldn't define it. But on the other hand, most Coloradoans can't tell you where the Indian Peaks are - even though they're a part of what we refer to as "the Front Range"! So, when someone who lives in Denver is going camping for the weekend - say, near Breckenridge - they don't tell their friends, "I'm going to the Tenmile Range". They don't even say, "I'm going to the Rockies". They just say, "I'm going to the mountains". This term is used to describe just about anyplace in the middle third of Colorado*. Of course, most communities located in this part of the state are not actually on a mountain, but rather in a valley between mountains. Nevertheless, these towns are considered to be "in the mountains" (blue area on the map).
A synonym for "the mountains" is "the high country". Seems to me this term is used frequently by weather forecasters, but not often by the average Coloradoan. It's kind of funny, because everyplace in Colorado is higher than most places in the rest of the country! But when Coloradoans say "high country", they're talking about the highest parts of the highest state. The distinction is made because, for example, a spring storm that might bring snow to the high country will often only rain on lower-elevation Front Range cities.
* The only exceptions I can think of (places that are in the central third of Colorado but are not considered "in the mountains") would be towns located in the San Luis Valley (shown in orange on the map). Though surrounded by the high mountains of the San Juan and Sangre de Cristo ranges, it's a huge and extremely flat area. You'd have to drive at least a half-hour out of Alamosa to get into any kind of mountainous terrain.
This is another non-specific reference that you won't find on a map. You see, most of the real high mountains (12,000 to 14,000 feet) don't just suddenly jut right up at the edge of the Plains. Instead, you'll find a narrow transition zone just west of the Front Range cities, characterized by lots of lower hills and interesting geographical formations. Locals refer to this terrain as "the foothills" (shown in red on the map). In other words, you pass through "the foothills" when travelling west from a Front Range city to get to "the Front Range". (I bet that clears things up...)
The Western Slope
To understand this term, you need to understand the Continental Divide. Basically, this is a chain of mountains and ridges that separates land draining west to the Pacific Ocean from land that drains east to the Atlantic Ocean. The Divide runs from Canada through the U.S. and Mexico to Central America - and actually all the way through South America, too, although that's a different continent. Anyway, the Continental Divide runs right through the middle of Colorado. This factors significantly into the lives of Coloradoans, particularly in terms of water. You see, most moisture in Colorado comes eastward from the Pacific. The high mountains squeeze out much of the rain and snow from these weather systems before they make it to the Front Range. So most of the water in the state drains westward - which unfortunately is away from where most Coloradoans live. As a result, we've built dozens of water projects over the years that transfer water to the east side of the Divide. In other words, water that would naturally drain into the Pacific is instead captured in reservoirs and delivered into Atlantic watersheds via ditches, pumps, and/or tunnels bored right through mountains. As you might imagine, this causes a lot of political tension between people who live on opposite sides of the Divide.
Now, the term "Western Slope" is used a couple different ways. In terms of water, anything west of the Continental Divide is by definition on the Western Slope - so, in other words, roughly the west half of the state. But when someone is said to live on the Western Slope, that means something a little different. Back to the example of Breckenridge: although the town is west of the Divide, most people wouldn't describe it as being "on the Western Slope". Rather, they'd describe it as being "in the mountains". The term "Western Slope" is usually reserved for places such as Craig, Meeker, Rifle, Grand Junction, Delta, and Montrose: places which aren't really in the highest mountains, but rather west of them (shown in green on the map). Note: it ticks them off when you refer to it as "the West Slope"!
So, how do Coloradoans refer to the remaining third of their state? Eastern Colorado is sparsely populated, the terrain is very flat, and most Coloradoans consider it bleak and boring: a somewhat hellish place to be endured on the drive to Chicago or Kansas City. So it doesn't have much of an identity. Some tourism types have tried to market it as "Colorado's Outback", but that hasn't caught on. Instead it's often referred to as the Eastern Plains, the High Plains, or simply "the Plains" (shown in yellow on the map). It so happens I love it out there, and I've got several webpages about locations on the Plains.
When a Coloradoan describes themselves as being "from the Springs", or as "going to the Springs" - which Springs are they talking about?
Hot Sulphur Springs?
Mineral Hot Springs?
Mt. Princeton Hot Springs?
Waunita Hot Springs?
Actually, they're referring to the city of Colorado Springs. Many of the other "Springs" - particularly the better known ones - are commonly referred to by their first names only: Glenwood, Manitou, Pagosa, Steamboat, etc. Idaho Springs is an exception, for obvious reasons.
When someone says they're going "to Loveland", sometimes it's wise to ask for specifics if it's not clear from the context. There's a city of Loveland in the northern Front Range. But there's also a ski area called Loveland which is nowhere near the city. It's in the mountains, at the foot of Loveland Pass, just east of the Eisenhower Tunnel on I-70.
Same deal with Berthoud: there's the town, just south of Loveland. But Berthoud Pass is on US 40 between Empire and Winter Park. Berthoud ski area (an on-again, off-again affair) is located at the summit of Berthoud Pass.
The Valley Highway
This term becomes more antiquated as time goes by, but many long-time Denverites still refer to Interstate 25 through the city as "The Valley Highway". That's what it was called when it was being built in the 1950s (before the interstate system was in place), because it follows the Platte River Valley through the central part of town.
The Boulder Turnpike
This is the U.S. 36 freeway between Denver and Boulder. It wasn't always free; you had to pay to drive on it when it was first built in the 1950s. Even though the tollgates were removed years ago, people still call it "the Turnpike".
Other Denver-area freeways
The U.S. 6 freeway west of downtown Denver is usually called the "6th Avenue Freeway" or simply "6th Avenue" (it's entirely a coincidence that highway 6 traffic is routed on 6th Avenue - and even some Denverites mistakenly believe that 6th Av on the east side of town is still US 6).
The segment of U.S. 285 between southwest Denver and C-470 is still commonly referred to as "Hampden", even though in that area 285 is a freeway which in some stretches runs along a slightly different alignment than the actual Hampden Avenue.
But most other freeways are simply referred to by their number: I-70, I-270, I-225, etc. Some traffic reporters try to be cute by calling I-225 "two-and-a-quarter", but that hasn't caught on with the general populace. By the way: wanna know a quick way to let everybody know you're from Southern California? Refer to a Denver-area freeway as "the 70", for example, or "the 225".
When Coloradoans say they're going "skiing", they're talking about snow and chairlifts. If a Coloradoan is going to a reservoir to be dragged behind a boat, that's called "water-skiing". I bring this up because in Texas (and I suspect in many other parts of the U.S.), the word "skiing" implies summertime and a speedboat. On the other hand, if a Texan is taking a winter vacation in Colorado, they say they're going "snow-skiing".