Okay, Water Trails West didsn't help at all. If you couldn't float a streamboat on it, the writers weren't interested, and above Pueblo the Arkansas ain't navigable.

However, R. L. Duffus, in The Santa Fe Trail (1930), has this to offer, for whatever it's worth:

"Gold was found in Colorado ten years after it had been discovered in California. There were two routes into Colorado after 1841, one leaving the Oregon Trail at Julesburg, the other following the Mountain Division of the Santa Fe Trail on to Pueblo and beyond. Later, there was a third, the so-called Smoky Hill route, going up the Smoky Hill fork of the Kansas... The discovery of gold in 1858 and the gold rush of 1859 sent many hundreds over the Arkansas route." (italics mine)

Heading due west from the Smoky Hill would land you close to Colorado Springs, considerably north of the Arkansas River route to Leadville.

Not much help, I'm afraid.

Sandy