Snowmass Mountain in the Maroon Bells Wilderness near Aspen
Northwestern Colorado is a region of the state of Colorado in the United States of America. It is a diverse area of both red rock mesas and snow capped mountain peaks, as well as the headwaters of the Colorado River. This Rocky Mountains region includes a majority of the state's most popular ski resorts, places like Breckenridge, Aspen and Vail. It is also home to the Western Slope's biggest city, Grand Junction.
East, by the Western Slope of the Rocky Mountains; This contours along the Continental Divide, an imaginary line that marks the flow of precipitation. Rain falling on the west of the Divide makes its way to the Pacific Ocean. Rain on the east makes its way to the Gulf of Mexico and the Atlantic Ocean.
South, The southern borders of Mesa, Pitkin and Summit Counties. This is an arbitrary line 50 to 100 miles south of the east-west running Interstate 70, stretching roughly from the western portal of the Eisenhower Tunnel in the east to the Utah state line in the west.
Region boundaries in Colorado tend to be somewhat controversial (even in day-to-day life in the state) and are done in an ad-hoc way here. If you're expecting to read about some destination in this article and can't find it, check in the neighboring Front Range, Southwestern Colorado, and even South Central Colorado sections to see if it's covered there.
This area is dominated by its geology. It is fairly evenly divided between some of the highest, snow-covered peaks in the Rockies and the beginning of the sandstone canyon and mesa country that is typical of the high-desert Colorado Plateau. The two biggest geologic features in Northwestern Colorado are the Western Slope of the Continental Divide and the mighty Colorado River, fed by the mountain snow of the Rockies and eventually carving out the Grand Canyon in Arizona.
The mountains are still growing, thrust upwards by a subducting tectonic plate that scientists hypothesize is situated at an odd angle. It explains why Northwestern Colorado is curiously free of any volcanoes similar to the Cascades in Washington and Oregon. (Although there has been volcanic activity in the past, and Northwestern Colorado is dotted with geothermal pools in places like Steamboat Springs and Glenwood Springs). Northwestern Colorado boasts Mount Elbert near Aspen. It rises 14,433 ft (4268m) above sea level and is the highest mountain in the entire Rocky Mountain range.
A geological formation characteristic of the mesa portion of the region are the Bookcliffs that are shown to good advantage around Grand Junction. A legacy of this geology is that the region is famous for its Jurassic-era fossils, found throughout the Morrison Formation. Dinosaur National Monument, along the Utah state line and extending into that state, was formed to preserve the enormous fossil beds found there, which are still yielding remarkable paleontological discoveries. Delta, just south of the region in Southwestern Colorado, as well as Grand Junction have large fossil quarries.
There is an economic divide, as well. Northwestern Colorado is a region of both small, struggling towns and high-end ski resorts (some of the richest and most expensive in the world). The ski resorts are a playground for jet-setting millionaires and billionaires, with multimillion dollar mansions and high costs of living. Outside of these pockets of excess are large rural areas, home to ranches and orchards. Northwestern Colorado is also where Colorado's Wine Country is located, the state's answer to Napa and Sonoma in California. Sizable portions of Northwestern Colorado are public lands owned by either the federal government or the state. So there are plenty of opportunities for hiking, camping, fishing, hunting, mountain biking, rafting and other forms of recreation.
Between 250 and 1300 AD, the Fremont people were the area’s first inhabitants. Their culture can still be glimpsed today in the many petroglyphs and pictographs they created on canyon walls in the mesa portion of the region. Circa 1500, the Ute nation moved into Northwestern Colorado.
With the conquest of the Aztec Empire in Central America in 1521, the Spanish formed the Viceroyalty of New Spain and claimed a large part of North America for themselves, including a nebulous region around Northwestern Colorado. The borders were not firmly fixed on a map, and the Spanish only managed to settle as far as South Central Colorado.
During the 19th century, the area was very much in dispute with a young nation, the United States. After the Louisiana Purchase of 1803, the U.S. claimed all the land south and west of the Arkansas River. Spain declared a large trade zone around its colony of Santa Fé de Nuevo Méjico, a claim the U.S. challenged. In 1806, Zebulon Pike led a U.S. Army expedition into the area, "discovering" Pike's Peak in the process, but Pike never reached as far as Northwestern Colorado. A contingent of Spanish cavalry apprehended and arrested the Pike expedition in South Central Colorado, eventually expelling them from New Spain. The U.S. relinquished its claim on the region as part of the purchase of Florida from Spain with the Adams-Onís Treaty of 1819.
In 1821, the Viceroyalty of New Spain successfully revolted, splitting with the Spanish crown. Northwestern Colorado may have become part of Alta California, a province in the new nation of Mexico.
Hoping to develop the area, Mexican officials opened the land up to mountain men, trappers and traders. Between 1821 and 1840, explorer Antoine Robidoux ventured through the region in search of beaver pelts. With this influx of adventurers and speculators came many of the men who would later lead U.S. Army expeditions and Government Surveying parties through the area: Kit Carson, "Pathfinder" John Charles Fremont and Captain John Gunnison.
In 1846, the U.S. Army invaded and defeated Mexico in the Mexican-American War. With the Treaty of Guadalupe y Hidalgo, the U.S. gained control of Northwestern Colorado, as well as California, Nevada, Utah, and portions of Arizona, New Mexico and Wyoming.
In 1849, the Mormons established the Provisional State of Deseret, which included parts of Northwestern Colorado, a claim the U.S. refused to recognize. For the next 20 years, the Mormons refused to settle east of the north-south running Green River.
While the U.S. was busy expanding its territory, the Utes were fighting a rear guard action, with intermittent settler encroachments on their lands. Friction between the Utes and whites over resources was inevitable. In 1868, the U.S. Government and the Ute Indians signed a treaty that designated Northwestern Colorado as part of the Ute reservation. But the area's rivers offered both a reliable source of water and arable land. This was compounded by the discovery of gold and silver in the San Juan Mountains to the south. There was also a missionary spirit amongst the whites, who saw it as a God-driven destiny to convert the nomadic Utes to Christianity and an agrarian way of life. These factors proved to be too great for the settlers to resist.
A meadow vole clears clods of dirt from its burrow in the Arapaho National Forest.
Determined to turn them into farmers, the head of the government's Indian Agency, Nathan Cook Meeker, approached the Utes with a mixture of arrogance and hostility. He plowed up a Ute horse-racing track to plant a field, and later engaged in a fist fight with the owner of the race track. In 1879, Meeker telegraphed for military assistance, and the Federal government responded with around 200 soldiers to police the area. The situation was handled with mutual mistrust on both sides, and several skirmishes occurred. The crisis culminated with the Utes killing several whites at the Indian Agency (including Meeker) and launching the so-called Ute War. Initially successful, the Utes were forcibly relocated to Utah, and Southwestern Colorado, near Cortez.
The Uncompahgre Reservation was opened to settlers in the fall of 1881. Settlers poured into the area. Towns like Paonia, Grand Junction, Meeker and Craig were rapidly established. For the next 80 years, farming and ranching were the staples of the region's economy. Mining towns like Aspen, Breckenridge and Leadville capitalized on the silver and gold bonanzas.
Post World War Two ushered in an area of unprecedented prosperity for Northwestern Colorado, with the founding of area's modern ski resorts. The second half of the 20th century witnessed the birth of Snowmass Village, Vail, Beaver Creek, Copper Mountain, Arapahoe Basin, Vail, and Keystone. Grand Junction grew into a regional hub to service the ski towns, as well as a boom and bust community of uranium and oil shale mining, and natural gas exploration. The population of this region continues to grow as people fall in love with its natural beauty and many recreational opportunities.
The area is largely English-speaking, with a handful of Spanish speaking communities like Minturn near Vail. There is a wide circle of Spanish speaking laborers who are the working class backbone of the mountain resorts, energy, construction and hospitality industries. At the opposite end of the spectrum are Central and South America's moneyed ruling class, who flock to Vail between Christmas and New Year's. See WikiTravel's Spanish phrasebook for more information on how to better engage both groups.
Also, within the ski towns, there are large, developed exchange programs with college-age students from Europe and South America. You will find them running the ski lifts and equipment rental shops, so hearing French, German, and Italian is not uncommon during the ski season. All, however, are required to speak English.
There are major airports in Denver and Grand Junction, and regional airports in Aspen and Vail.
Denver International Airport, (IATA: DEN, ICAO: KDEN). Commonly referred to as DIA. It is located about 20 miles to the east of downtown Denver. Frontier Airlines, United Airlines, and Southwest Airlines all maintain hubs at the airport in Concourses A, B, and C respectively. Most other major domestic carriers also have service here.
Grand Junction Regional Airport, (IATA: GJT, ICAO: KGJT), otherwise known as Walker Field, is served by six airlines with nonstop service to Dallas/Fort Worth, Denver, Salt Lake City, Phoenix, and Las Vegas. Some service is seasonal. For private pilots, it is also possible to fly your small plane into the airport and leave it while you tour the area. Taxi service is also available at the airport.
Aspen-Pitkin County Airport, (also known as Sardy Field) (IATA: ASE) (ICAO: KASE)), . Major carriers to Aspen include United, US Airways, Delta Airlines, and Frontier Airlines. ASE is a small airport for small planes only, and traffic tends to stop in any inclement weather.
Vail/Eagle County Airport (IATA: EGE, ICAO: KEGE). Phone: +1-800-225-6136, Located 20 minutes west of Vail in Eagle.
Yampa Valley Regional Airport, (also known as Yampa Valley Airport) (IATA: HDN) (ICAO: KHDN)), . Major carriers to Steamboat include American, Continental, Delta, Frontier, Northwest and United. Some service is seasonal.
Aspen - About 4 hours from Denver on Interstate 70. There are two major routes from Denver - through Glenwood Springs or through Independence Pass. Independence Pass is only open in the summer months, but provides spectacular views and can be a bit faster than the longer route through Glenwood. To take this route, travel south from Copper Mountain and exit off I-70 to Leadville.
Breckenridge - About 90 minutes west of Denver. Travel on I-70 West for 71 mi (114 km). Take exit 203 for CO Hwy 9 South toward Breckenridge/Frisco. At the traffic circle, take the 4th exit onto CO-9 heading to Frisco. Travel 10 mi (16 km) to Breckenridge.
Grand Junction, Clifton and Palisade - Palisade and Grand Junction are on Interstate 70, about 40 minutes east of the Utah border and 4 hours west of Denver. From the South, (Telluride, Delta and Montrose), drivers can travel US 50 north.
Steamboat Springs - Typically 3 to 4 hours away from Denver by car in good winter conditions. If heavy snow, there are a couple of passes (including Rabbit Ears Pass) which become much more difficult and slow going. The most direct route from Denver to Steamboat is I-70 west to Silverthorne. From there, take Hwy 9 North to Kremmling where you meet up with US 40. Then drive west on US 40 over Rabbit Ears pass to Steamboat. With no traffic or snow, the drive can be as quick as 2.5 hours.
Vail- 100 mi (161 km) west of Denver on Interstate 70, and about 130 mi (160 km) from Denver International Airport.
Amtrak serves Grand Junction and Glenwood Springs with the California Zephyr, which runs daily between Emeryville (in the San Francisco Bay Area) and Chicago. Amtrak and AAA partner to run several Wine Trains between Denver and Grand Junction each spring. 
Wildlife viewing comes in all sizes in Northwestern Colorado: A Whitelined Sphinx Hummingbird Moth sips nectar from a Columbine (the state flower) in the White River National Forest.
The major artery through the region is Interstate 70. Weather-wise, there are three distinct micro-climates along I-70 in Northwestern Colorado. Conditions are highly variable depending on both the altitude and terrain. The weather can be blizzard conditions on the Eastern Slope of the Continental Divide in South Central Colorado, cloud cover on the Western Slope, and sunny west of Glenwood Canyon near Glenwood Springs.
During the winter, heavy ice and snow are a concern on the mountain passes, which can make driving difficult and slow going. Always check the weather and road conditions  before heading out. Even on a clear winter's day, make sure your vehicle's wiper fluid reservoir is full. The Colorado Department of Transportation (CDOT)  spreads both sand and magnesium chloride on the roads, which makes for an impenetrable, gluey mess on your windshield.
In the summer months, it's not uncommon to see the shoulders of the highways littered with broken-down vehicles that could not handle the steep grades and high altitude air of the Rocky Mountains. If you are venturing from a lower altitude, make sure your car can handle mountain driving. Thinner air means you will be burning more gasoline. Also, with so many steep grades, expect to gear down to avoid unnecessary friction to your brake pads.
During peak times, I-70 can get very crowded and it is not unheard of for a trip from Eagle and Summit Counties to Denver to take 3 hours or more (Allow for 5 from Pitkin County). Peak times are weekend afternoons (2 pm- 6 pm) both in the summer and winter. Plan accordingly and either leave in the morning, or leave after 5 pm in the winter.
Buffalo Pass - Near Steamboat Springs. Only road crossing the Continental Divide through the Park Range. Offers great views of the Yampa River Basin. Dirt road popular for fat tire bike rides and four wheel drives.
Canyon Pintado - Driving tour of Fremont petroglyphs and pictographs, near Rangely.
Glenwood Canyon - View rugged canyon walls along a masterfully engineered highway. Bike and hiking trails parallel I-70. Near Glenwood Springs.
Independence Pass - High mountain drive is only open in the summer months. Between Leadville and Aspen.
Loveland Pass - Before the I-70 Eisenhower Tunnel was built, this above timberline road was the original highway over the Continental Divide to get to the ski resorts. Between Georgetown and Silverthorne.
There is no shortage of summer or winter activities in this diverse wilderness area.
Arrange for a horse drawn sleigh or dog sled ride. Usually comes with hot chocolate or spiced cider. Aspen, Vail and the resorts around Summit County have outfitters who will take care of everything for you.
Go ice skating on an outdoors rink or groomed municipal pond.
Ride a ski lift, quad chair or gondola to the top of one of the ski slopes in the summer months. Many resorts, like Vail's Eagle's Nest, offer modest grilled food at the summit. You can then hike, bike or ride the lift back to the bottom.
River runners will enjoy the various rapids along the Yampa, Colorado, Frying Pan, Eagle and Roaring Fork Rivers. There are outfitters in all the resort towns, Grand Junction and Glenwood Springs.
For wine tasting tours, head to Palisade or Grand Junction, home of the Grand Valley American Viticultural Area (AVA).
There's no reason to fear the mountains, as long as you approach them with proper respect and preparation. As with anywhere else, recklessness and a lack of forethought can get you into trouble, especially in Colorado's vast back country.
Altitude sickness - Can lead to dizziness, headaches, nausea, even blackouts and pulmonary edema. Give your body a few days to adjust to the high altitudes before going full throttle with your hiking or skiing.
Dehydration - When you engage in strenuous outdoor activities, be sure to replenish your fluids as you go. You may be losing moisture through your mouth and nose and through sweating, but be completely unawares due to the arid mountain air. May result in dizziness, intense thirst and elevated heart and breath rates.
Giardia - Drinking untreated water from regional streams is not a good idea owing to Giardia parasites, but tap water is not a problem.
Hypothermia - Prolonged exposure to the cold can result in confusion, a slowed heart rate, lethargy, even death. Dress warmly in non cotton clothing to allow any sweat to wick away from your body and evaporate. Otherwise, it may thoroughly chill you later in the day when temperatures drop.
Frostbite - During periods of severe cold, your circulatory system pulls all your warming blood into the core of your body to protect your vital organs. This makes your extremities such as your ears, fingers and nose especially vulnerable. Wear a face mask, insulated gloves and other heavy gear on the worst winter days. It gets cold sitting still on those ski lifts!
Sunburn - Lather up with sunscreen, even if there's cloud cover. Colorado's high elevation means you have less protection to the sun's powerful ultra violet rays. This can be compounded while skiing or snowboarding, when the rays are reflected off the snow and hits the underside of your jaw. Don't forget to wear UV-rated goggles or sunglasses, as well. There's nothing more painful than sunburned eyeballs.
Avalanches - Colorado claims about a third of all avalanche deaths in the U.S. The ski resorts have groomed slopes that are are safe, but it is extremely dangerous to ski or snowboard outside of the designated terrain. It's popular amongst daredevil skiers to "run the chutes," steep, shaded slopes that funnel into tight gullies. These are classic avalanche zones. Far more common (and deadly) are slab avalanches that break along a fault line and bury unsuspecting snow mobilers or skiers. Always wear a homing beacon and check the conditions at the Colorado Avalanche Information Center before heading into the back country.
Lightning - This is especially deadly in the high country above timberline when no shelter is nearby. If you hear crackling or hissing sounds, or your hair begins to stand on end, squat down immediately in the "lightning desperation position" - feet together and your hands clapped over your ears. Remember, a tent and inflatable mattress offer no protection from a lightening strike. Avoid the high ground, or solitary objects like trees that stick out higher than the surrounding terrain (they may act like natural lightning rods). For more information, see the safety tips at the National Oceanic and Atmospheric Agency (NOAA) .
Arches National Park - Largest concentration of natural arches in the world, just northeast of Moab in Utah, as well as other strange sandstone formations, such as pinnacles, cliffs, mesas, and gorges.
Hovenweep National Monument - Near Cortez. Protects six Ancestral Puebloan villages spread over a twenty-mile expanse of mesa tops and canyons along the Utah-Colorado border. Iconic to the monument are the multi-storied ruins.
Yucca House National Monument - Near Cortez. An entire unexcavated city of Ancestral Puebloan houses, built between 1150 and 1300 A.D.
This is a usable article. It gives a good overview of the region, its sights, and how to get in, as well as links to the main destinations, whose articles are similarly well developed. An adventurous person could use this article, but please plunge forward and help it grow!