It's Summer, so a Bit of Gold Rush History...

Recorded history is a recent thing for much of the American West, although inhabited for perhaps 12,000 to 14,000 years by indigenous peoples.

As was the case for other areas such as California, the discovery of gold triggered an in-migration of new settlers. The earliest report of gold in what would become the Denver metro area happened in 1850, at Ralston Creek, at its confluence with Clear Creek, which drops out of the Rocky Mountains. 

Lewis Ralston, a Georgia prospector headed for the California gold fields, found about a quarter  ounce (6 grams) of gold at what became Ralson Creek. Ralston's companions named the stream Ralston's Creek in his honor, but they all left the next morning for the California gold fields. 

Here is that spot today. 

source: Wikimedia

The founding of Denver, Boulder and other towns did not happen until after 1857, though. 

“A May 1857 discovery of gold-dust by George Simpson in Cherry Creek near its confluence with the South Platte River and the discovery of gold nuggets near the future site of Denver by Fall Leaf, a Delaware Indian working as a U.S. Army scout, sparked Midwestern and Eastern interest in the western fringe of Kansas Territory,” according to the Colorado Encyclopedia. 

In 1858 the Russell brothers—William, Oliver, and Levi, along with John Beck and a party of Cherokees and whites from Georgia--reached Ralston Creek where they found a little gold. 

They then headed upstream (south) along the South Platte, past Cherry Creek and on to Little Dry Creek in present-day Englewood, where they found paying quantities of placer gold. 

The towns of Auraria, Denver, Boulder and Golden were founded over the next several years. 

Here is a view of downtown Denver, looking east, at the confluence of Cherry Creek and the South Platte river, where gold was discovered in 1857.  Below is it is the same area, as painted about 1858, looking west. Northern Arapahoes in the foreground, I think. 

source: Lonely Planet

Here is the same confluence, during the 1930s, when people continued to pan for gold. It was the discovery of gold in Cherry Creek--at about the confluence--about 1857 in this area that lead to the founding of Denver. 

source: Reddit

Casual, manual gold panning still is possible in the metro Denver area, so long as landowner permission is given, often by the local park and recreation districts or the water companies.