Here is an article that actually describes the search for the mercury in the laxatives: https://www.discovermagazine.com/following-lewis-and-clarks-...

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ljlolel 5 days ago | parent [-]

Out of the more than 600 potential locations Lewis and Clark stopped at, only one has been verified by mercury analysis: Travelers’ Rest in Lolo, Montana. We know from their journals that the Corps visited on two occasions. The first was in mid-September of 1805, after attempting to pass over the Bitterroot Mountains and being forced back by deep snow. Then they returned at the end of June and into early July of 1806, on their way back east.

	▲	dboreham 5 days ago \| parent [-]
		Finding the locations for their camps is tricky. They passed within a mile of my house and I've spent some time trying to identify the trail route and camp site. However the journals turn out to be mostly very brief, lacking sufficient detail. Also all the geographic feature names they use are different than today's, so you need a translation map for those, which in turn may be inaccurate.