Colorado is also one of only four states in the United States to share a common border (Four Corners), along with Arizona, New Mexico and Utah. At this intersection, it is possible to stand in four states at once.
The climate of Colorado is quite complex compared to most of the United States. The typical south-north/cooler-warmer variation in other states is not generally applicable in Colorado. Mountains and surrounding valleys greatly affect local climate. As a general rule, with an increase in elevation come a decrease in temperature and an increase in precipitation. A main climatic division in Colorado occurs between the Rocky Mountains on the west and the plains on the east; the foothills form a transitional zone between the two.
The climate of the Eastern Plains is a semi-arid continental climate (Koppen climate classification BSk) of low humidity and moderately low precipitation, usually from 10 to 15 inches (250 to 380 mm) annually. The area is known for its abundant sunshine and cool clear nights, which give this area the highest average diurnal temperature range in the United States. In summer, this area can have many days above 95 °F (35 °C) and sometimes 100 °F (38 °C), although 105 °F (41 °C) is the maximum in the front range cities above 5000 ft (1500 m). In those areas, ?25 °F (?31.7 °C) is the all-time record low. About 75% of the precipitation falls within the growing season, from April to September, but this area is very prone to droughts. Most of the precipitation comes in the form of thunderstorms, which are often severe, and the form of major snowstorms that happen most often in the early spring and in late autumn, and sometimes winter, from low pressures that bring the right conditions. Otherwise, winters tend to be drier and cold, even though it's known for having a number of mild days in many winters. In much of this region, March and April are the snowiest months. April and May are normally the rainiest months, while April is the wettest month that has the most combination of rain and snow. The Front Range cities closer to the mountains tend to be warmer in the winter due to chinook winds which warm the area, sometimes bringing temperatures up to 60 °F (16 °C) or higher in the winter. The average July temperature is 57 degrees in the morning and 87 degrees in the afternoon. The average January temperature is 15 degrees in the morning and 43 degrees in the afternoon, although the daily high may be 60 one day and 0 the next.
West of the plains and foothills
West of the plains and foothills, the weather of Colorado is much less uniform. Even places a few miles (kilometers) apart can experience entirely different weather, depending on the topography of the area. Most valleys also have a semi-arid climate, which becomes an alpine climate at higher elevations. Generally, the wettest season is in the winter in Western Colorado while June is the driest month, which is the opposite of precipitation patterns in the east. The mountains have cool summers with many days of high temperatures around 60 °F (16 °C) and 70 °F (21 °C), although frequent thunderstorms can cause a sudden drop in temperatures. Summer nights are cool, and cold at the highest altitudes which can sometimes bring snow even in the middle of the summer. The winters bring abundant, powdery snowfall to the mountains which the skiers love, although even in the winter, there can be many days with abundant sunshine in between major storms. The Western Slope has high summer temperatures similar to those found on the plains while the winters tend to be slightly cooler due to the lack of any warming winds which are common in the plains and Front Range. Other areas in the west have their own unique climate. The San Luis Valley is generally dry with little rain or snow, although the snow that falls tends to stay on the ground all winter.
Extreme weather is a common occurrence in Colorado. Thunderstorms are common east of the Continental divide in the spring and summer, and Colorado is one of the leading states in deaths due to lightning. Hail is a common sight in the mountains east of the divide and in the northwest part of the state. While not as common as some of the states to the east, much of the Eastern Plains are prone to tornadoes, and there have been some damaging tornadoes there. An example is the 1990 Limon F3 tornado and the 2008 Windsor F3 tornado which devastated the city. Floods are also a factor in the plains, not just from the thunderstorms, but also due to heavy snow in the mountains followed by a warm, dry period which swells rivers with melted snow. In 2008, from July through August, a new record was set that was previously held in 1901 of twenty-three straight days of 90 degree heat, surpassing the previous record by almost a week. Colorado is also known for its droughts that occur every few years, causing major wildfires such as the Hayman Fire, one of the largest wildfires in US history.
The highest temperature ever recorded in Colorado was 118 °F (48 °C) on July 11, 1888, at Bennett, while the lowest was -61 °F (-52 °C) on February 1, 1985, at Maybell.
The region that is today the State of Colorado has been inhabited by Native Americans for more than 13 millennia. The Lindenmeier Site in Larimer County contains artifacts dating from approximately 11200 BCE to 3000 BCE. The Ancient Pueblo Peoples lived in the valleys and mesas of the Colorado Plateau. The Ute Nation inhabited the mountain valleys of the Southern Rocky Mountains and the Western Rocky Mountains. The Arapaho Nation and the Cheyenne Nation moved west to hunt across the High Plains.
The United States acquired a territorial claim to the eastern flank of the Rocky Mountains with the Louisiana Purchase from France in 1803. The U.S. claim conflicted with Spain's claim that a huge region surrounding its colony of Santa F? de Nuevo M?jico was its sovereign trading zone. Zebulon Pike led a U.S. Army reconnaissance expedition into the disputed region in 1806. Pike and his men were arrested by Spanish cavalry in the San Luis Valley the following February, taken to Chihuahua, and expelled from M?xico the following July.
The United States relinquished its claim to all land south and west of the Arkansas River as part of the U.S. purchase of Florida from Spain with the Adams-On?s Treaty of 1819. M?xico finally won its independence from Spain in 1821, but it surrendered its northern territories to the United States after the Mexican-American War with the Treaty of Guadalupe Hidalgo in 1848. In 1849, the Mormons of Deseret (now Utah) organized the extralegal Provisional State of Deseret which claimed all landdrained by the Green