So where did all this gold come from anyway?

The gold in metro Denver is in almost every waterway big enough to have a name. In the early days of the gold rush this was confusing and frustrating for the first American prospectors. They found gold way out southeast in Elbert County, due south of what’s now Denver in Douglas County and Arapahoe County…and right in downtown Denver. Of course that’s why Denver is where it is!

However each of these deposits was quickly shown to be too small to make the miners rich. They also couldn’t find the hard rock sources of the gold. This meant many of the first serious prospectors in 1858 gave up and went back east. Of course we know there’s lots of gold in the mountains of Colorado …as the more tenacious prospectors found for themselves in 1859!

Here’s an early map showing the important early towns. It illustrates the locations focused on by the first migrant prospectors:


Places like Frank’s Town (now Franktown) and Russelville (not really a place any longer) were important early gold discoveries in the summer of 1858 but were declared a “hoax” by that fall.

The geologic story behind this is that there are multiple origins of the gold in metro Denver. The obvious source is the mountains just west of town. This gold was washed down via the South Platte River (unlabeled above but running north thru Denver, shown as a wide line on the map) and via smaller waterways such as Clear Creek (called Vasquez Cr. On the map) and Ralston Creek. The confusing part is the gold in Cheery Creek (now called Cherry Creek) running throug Franktown and Russelville. It actually originates from mountains long weathered away As the Rockies formed during the later part of the time of the dinosaurs. These mountains left a layer of river cobbles and gold bearing sediments in our soil called the Castle Rock Formation. This thick layer of conglomerate rock can be easily seen today as the cap layer on the Castle Rock next to the town of the same name.

Castle Rock Colorado, landscape
The Castle Rock just east of the eponymous town.

The interesting part for prospectors lies in the fact that this layer of gold bearing rock once covered virtually all of south metro Denver from the Castle Rock area north almost to the edge of the city of Denver. It stretched from the edge of the foothills on the west, all the way into the western part of Elbert County in the east. Of course, across most of this area, the gold bearing rock is long since decomposed and is often buried under a thick layer of sand in the east or clay in the west. This means there’s a layer of gold bearing material under many homes and businesses in south metro Denver and it’s been laying there as placer gold for tens of millions of years!

Cool but “so what?” You say? Well, in many spots, this gold layer is close to the surface or even on the surface. This naturally means it is cut through by local creeks and there is the possibility of finding honey holes where those modern creeks have concentrated the gold from the material they washed away over the last thousands of years. These creeks feed into the South Platte in their turn and are also important contributors to the gold in the South Platte through metro Denver and north from there. Of course the South Platte itself gathers and reconcentrates this gold as well. What confused the original American prospectors can be great information for us…and a fun, productive source of gold as well!

I’ve had very good success prospecting the smaller waterways of south metro Denver and you can too. If you go looking please:

1. Know who owns the land and get permission or follow the rules on locally owned public lands.

2. Leave sites as you find them so as to avoid inspiring complaints from other users of recreational open space.

3. Pick up trash and be friendly to those you meet – be a good ambassador and guest!

4. Keep in mind that most of these spots are very small and can’t support many visitors at once.

5. Above all, avoid being that one bad apple whose action leads to prospecting and rock hounding being banned in an open space park!!

As always, I look forward to your thoughts and questions via comments here, emails or Facebook comments on the Facebook group “Finding Gold in Colorado”.

Just for fun, here’s shots of gold I found in the little creeks of south metro Denver:

By the way each of these pics documents my result from 1-2 hours of digging and feeding a sluice. Yup, there’s good gold in South metro Denver. Go get yours!

Here’s some interesting geology detail:

Cover page

 

Front Range geology cross-section. The top layer of rock on the right side of the image is our conglomerate. 

 

 

 

 

 

 

 

 

 

For geology geeks, dive deeper with this PhD thesis from 1933: https://dspace.library.colostate.edu/bitstream/handle/11124/170443/T546.pdf?sequence=1&isAllowed=y

One note: The thesis research focused exclusively on the area east of the town of Castle Rock. However we now know the castle rock formation extended further west almost to the current bed of the South Platte River and is gold bearing across that whole area.

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