Lewis and Clark arrived at Belle Fountaine, just west of the confluence of the Missouri and Mississippi Rivers.

From Sgt. Ordway's journal...
"towards evening we arived at Bell fountain a Fort or cantonement on South Side which was built since we ascended the Missouri & a handsome place. we moovd. a short distance below and Camped, the Company of Artillery who lay at this fort fired 17 Rounds with the field peaces the most of our party was Quartered in the Canonment."

To give you some idea of difference in going out and coming back..
1. Took a year and a half to get there. Averaged like 14 miles a day going against current. Also was pulling an 18 ton keel boat the first spring.
2. Took 7 months to get back. Often traveling 60 -75 miles a day with the current.

I'm willing to bet most of that 7 months on the return trip was spent hiking from the mouth of the Columbia River east until they got over the Continental Divide.

Just doing a little top of my head math - at 60 miles a day, that's 1800 miles in a month. That should get you from Montana (headwaters of the Missouri River) to Belle Fontaine in a month, maybe just over. Which leaves 5-6 months of hoofing it from Oregon to Montana. Although I do believe they were delayed some by snow, because they started too early in the year.

Smeghead4761 said:

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I'm willing to bet most of that 7 months on the return trip was spent hiking from the mouth of the Columbia River east until they got over the Continental Divide.

Just doing a little top of my head math - at 60 miles a day, that's 1800 miles in a month. That should get you from Montana (headwaters of the Missouri River) to Belle Fontaine in a month, maybe just over. Which leaves 5-6 months of hoofing it from Oregon to Montana. Although I do believe they were delayed some by snow, because they started too early in the year.

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There was very little hiking as they had horses waiting for them with the Shoshones when they left the Snake River and head back across the Bitterroot Mountains. They were on the Yellowstone River and then on the Missouri. They didn't average 60-75 miles a day but did cover this distance on good days.

Yeah 60 miles a day on foot is a grueling pace. One of the fastest historic western treks I am aware of was Stephen Kearney's march to Santa Fe at the beginning of the Mexican War. They were trying to get there before the city found out about the war from Mexico City and they only travelled 25 miles per day.