It is important to know that in Colorado, there is a mineral belt. Having a claim within the mineral belt is important, and while it is possible to find gold outside of the mineral belt, these scenarios should be considered anomalies and not the norm.
Boulder County: Boulder county is located in the front Range, North West of Denver and ranks ninth among the gold-producing counties of Colorado. Gold is the primary metal produced in the county, but much silver and tungsten and small amounts of lead and copper have also been mined at production levels. Through 1959, Boulder County had an output of about 1,048,200 ounces of gold.
Thomas N. Nolland wrote about the Central mining district in Boulder county "The district produces the richest gold and silver ore found in the world ; ores worth as high as $200,000 per ton. (at the price of gold back then, that would be 10,000 oz/T ) The veins are true fissures, producing all the different varieties of gold and silver ores, free milling, smelting and concentrating, carrying gold, silver, iron, copper and lead." Some of the important mines in Boulder county are the Golden age, Grand Central, Bueno, Burlington, Cold Spring mine, There are only a handful of mining districts that were large gold producers, Those were Jamestown (Central), Gold Hill/Sugarloaf, Ward, Magnolia, and Grand Island/Caribou.
Gilpin County: Located approximately 30 miles west of Denver, Gilpin county ranks second among the counties of Colorado in gold production, although Gilpin County is one of Colorado's smallest counties, both in land area and population with approximately 5,491 residents. Through 1959 the county produced a staggering 4,255,000 ounces of gold. From this production, 4,207,000 ounces was from lode gold and 48,000 ounces was from placer gold production. Gilpin County is home to "The richest square mile on earth" which is Central city and Blackhawk, now a popular gambling hot spot. The first smelter came to the county 9 years after gold was discovered in the county. This County is home to some very productive mining operations running to this day. There is still millions of ounces left in this county.
Other Counties: On this page I have not included gold production numbers from other counties because I currently have no claims in other counties. I have prospects that I am working on that may end up being viable claims but I am not to that point on these prospects.