[South Platte River Near the Rocky Mountains] October 28th 1858 dateline on important letter of E.P. "Pinkie" Stout addressed to his future wife, Miss Kirk, Cherry Fork PO, Ohio, cover franked with 3c Dull Red (#26) was carried privately as described in his letter, it entered the mails with Pacific Iowa December 4 postmark, original four page letter:

".... An officer of the army at Ft. Kearney, who came out with us returns tomorrow and will take our letters there & mail them from which place the mail runs once a week to the states. We reached our place of destiny yesterday, and our little party of nine met with a very favorable reception. … two old mountaineers who have lived in the mountains for 27 years & traded with the Indians (William McGaa, aka “Jack Jones” and John Smith) After we had camped near them they came over and invited us all to come over the their lodges (of the Indian stile) and eat a rib with them we readily assented …. There one of his squaw wives (Wenona) was called and after a little conversion between them in Indian She withdrew & appeared with a large tin vessel containing, a warm whiskey toddy sugared & spiced to the highest flavor. Of course we all partook, some more & some less (suffice it to say I didn’t get drunk) … we were then asked if we would be helped to some of the dog to which as a matter of courtesy we all consented. ... We are located on the South Platte near the point (8 miles) from where the stream comes through the Mountains...Tomorrow I start out on a prospecting tour will be gone 4 or 5 days will follow up cherry creek into the mts...I will send you a specimen of the gold found here it is said to be the virgin gold & worth $20 pr ounce, the coarse gold or quartz rock has not yet been discovered...Our man cries out for letter & am forced to close. Mag write often and direct your letters 1/2 to Ft. Kearny and 1/2 to Ft. Laramie Nebraska Ter in order that I may get some of them.."
 

The earliest reported cover from the Colorado gold mines, ex Risvold and Walske
Illustrated in MWE, Figure 12-3.