There's gold in, yes IN, downtown Denver! Thats why they built the city where it is after all. Also in waterways all over metro Denver....
You can walk to gold in Cherry Creek a block or two from the Colorado Convention Center...and shovels, pans and sluices are allowed. Depending on your timing, I might even be able to come along if you want.
I know lots of people pan the river near the junction of 36 & I 76. At that time of the year though it may be 70 degrees or you might be in a snow storm! The water temp will be cold!