The region that is today the state of Colorado has been inhabited by the Ancient Pueblo Peoples who lived in the valleys and mesas of the Colorado Plateau. The Ute Nation inhabited the mountain valleys of the Southern- and Western Rocky Mountains, even as far east as the Front Range of present day Colorado. Other peoples were the Apache, the Comanche, the Arapaho Nation and the Cheyenne Nation.
The United States acquired a territorial claim to the eastern flank of the Rocky Mountains with the Louisiana Purchase from France in 1803. This U.S. claim conflicted with the claim of Spain to the upper Arkansas River Basin as the exclusive trading zone of its province of Santa Fé de Nuevo Méjico.
The United States relinquished its claim as part of its purchase of Florida from Spain with the Adams-Onís Treaty of 1819. The treaty took effect 22 February 1821. Spain finally recognized the independence of Mexico with the Treaty of Córdoba signed on 24 August 1821. Mexico eventually ratified the Adams-Onís Treaty in 1831. The Texian Revolt of 1835–1836 fomented a dispute between the United States and Mexico which eventually erupted into the Mexican-American War in 1846. Mexico surrendered its northern territory to the United States with the Treaty of Guadalupe Hidalgo at the conclusion of the war in 1848.
On 28 February 1861, outgoing U.S. President James Buchanan signed an Act of Congress organizing the Territory of Colorado. The original boundaries of Colorado remain unchanged today. The name Colorado was chosen because it was commonly believed that the Colorado River originated in the territory.
The U.S. Congress passed an enabling act on 3 March 1875, specifying the requirements for the Territory of Colorado to become a state. On 1 August 1876, U.S. President Ulysses S. Grant signed a proclamation admitting Colorado to the Union as the 38th state.
After the organization of the Territory of Colorado and William Gilpin had been duly installed as the first governor, a design of a seal was entrusted to the Secretary of the Territory, L.C. Weld, with instructions to submit his rough draft to Governor Gilpin. It appears that the Governor approved the suggestions Weld had incorporated but said that there should be a suitable and appropriate motto. Weld, according to the stoy said, ‘Well, Governor, what would you suggest?’ Gilpin thought a moment and replied, in his own peculiar style, ‘Nil Sine Numine.’” 
On Nov. 6, 1861, the first Territorial Assembly of Colorado passed a law creating Colorado's circular Seal. This showed a coat of arms
Arms: Or, a hammer and a pick in saltire Sable and a chief Gules, three snow-capped mountains Azure and Argent.
Crest: The Eye of Providence and a fasces wrapped with a ribbon Gules, Argent and Azure, the white inscribed UNION AND CONSTITUTION. per fess proper.
Motto: NIL SINE NUMINE (Nothing without the Deity).
...surrounded by the legend: SIGILLUM TERRITORII COLORADENSIS 1861 
Of this first seal no picture is available but the arms were of about this shape:
Seal of 1877
In 1876, the voters adopted the state constitution as part of the requirement for federal approval of statehood for Colorado. Article 4, Section 15 of the constitution read:
"There shall be a seal of the state, which shall be kept by the secretary of state, and shall be called the 'Great Seal of Colorado'. The seal of the territory of Colorado as now used, shall be the seal of the state, until otherwise provided by law."
This seal of the State of Colorado was adopted by an act of the State legislature on 15 March 1877, the law going onto effect on 13 June 1877. The act reads:
“The seal of the State shall be two and a half inches in diameter, with the following device inscribed thereon: An heraldic shield bearing in chief, or upon the upper portion of the same, upon a red ground, three snow-capped mountains; above, surrounding clouds; upon the lower part thereof, upon a golden ground, a miners’s badge, as prescribed by the rules of heraldry; as a crest above the shield, the eye of God, being golden rays proceeding from the lines of a triangle; below the crest and above the shield, as a scroll, the Roman fascews bearing upon a band of red, white and blue the words, ‘Union and Constitution;’ below the whole to be surrounded by the words, ‘State of Colorado,’ and the figures 1876.” 
The Motto NIL SINE NUMINE (Nothing without the Deity [God]), is an adaptation from Virgil’s Aeneid Book II, line 777: ... non haec sine numine devum eveniunt.
At present the seal is usually represented full colour:
HEADQUARTERS, STATE AREA COMMAND
COLORADO ARMY NATIONAL GUARD 
Description: That for the regiments and separate battalions of the Colorado Army National Guard: From a wreath of colors, a fasces paleways Proper with ribbon of red, white and blue.
Symbolism: The fasces appears on the seal of the State. It is a bundle of rods with a battle axe bound together with the ribbon. It was a symbol of authority in the Roman Republic. Singly the rods are easily broken, bound together they are unbreakable.
Background: The crest for color bearing organizations of the State of Colorado was approved on 6 March 1922.
Distinctive Unit Insignia.
Description: A gold color metal and enamel device 3.02 cm in height consisting of a gold shield bearing a crossed pick and sledge hammer with black heads and brown handles and above them on a scarlet chief three blue mountains with white peaks; inscribed on a gold scroll below the shield the motto "NIL SINE NUMINE" in black letters.
Symbolism: The shield and motto are adapted from the Colorado State seal. The snow-capped mountains represent the rugged land of Colorado and the pick and hammer symbolize the importance of mining in the state. The gold of the shield alludes to the state's precious metal production. The meaning of the motto is "Nothing Without Providence."
Background: The distinctive unit insignia was originally approved for Headquarters and Headquarters Detachment and noncolor bearing units of the Colorado Army National Guard on 3 May 1971. The insignia was redesignated effective 30 December 1983, for Headquarters, State Area Command, Colorado Army National Guard.
Shoulder Sleeve Insignia.
Description: Centered on a disc 5.40 cm in diameter overall composed of three horizontal stripes of equal width of blue, white and blue, a yellow disc 1.59 cm in diameter within a scarlet letter "C" edged with white, and all within a 32 mm white border.
Symbolism: The design is taken from the Colorado State flag.
Background: The shoulder sleeve insignia was originally approved for Headquarters and Headquarters Detachment and other nondivisional units, Colorado National Guard on 4 November 1955. The insignia was redesignated with description amended for Headquarters, State Area Command, Colorado Army National Guard on 30 December 1983.
© Hubert de Vries 2013-12-23
 Zieber, Eugene: Heraldry in America. Published by the Department of Heraldry of the Bailey, Banks and Biddle Company. Philadelphia, Pennsylvania, 1895. P. 115. Shankle, Georg Earlie: State Names, Flags, Seals, Songs, Birds, Flowers and other Symbols. New York, 1951. Pp. 184-185.
 Laws of Colorado, 1861: General Laws, Joint Resolutions, Memorials, and Private Acts. Passed at the first Session of the Legislative Assembly of the Territory of Colorado, Begun and Held at Denver, Colorado Territory, September 9th, 1861 (Thomas Gibson, Colorado Republican and Herald Office, Denver, Colorado, 1861) p. 514.
 Colorado General Statutes 1883: The General Statutes of the State of Colorado, 1883.... Authorized by the fourth General Assembly (Times Steam Printing and Publishing House, Denver, Colorado, 1883) pp. 913-914.
 Retrieved from the site of the American Institute of Heraldry.