he reference points that made up the bulk of the notations in the Journals were often given as follows: ". . . a pt. on L.S. high Land psd. the head of an Isd. above is a large Sand bar on L.S.". This identifies a high point of land on the larboard side of the boat ("L.S."), just beyond ("psd." = "passed") the upper portion or "head" of an island ("Isd.") on the left. Normally, the captains used "larboard" and "starboard" to mean the left and right side of the boat.
Occasionally, they referred to the left or right banks of the river but this did not necessarily mean the bank on the left or right side of the boat. For river travelers in the early nineteenth century, the convention was to name the banks of a stream based on the direction in which the stream was flowing. For a stream flowing from the north, then, the right bank was the west bank, on the right hand side of someone traveling south down the river.
For Lewis and Clark, on their upstream journey, the left and right banks of the Missouri were to the right and the left respectively of the boat. In other words, the right bank of the Missouri (to Lewis and Clark) was the bank on their left as they proceeded upstream, on their right as they proceeded downstream. Those who followed immediately after Lewis and Clark were much less confused than we are about this system and the "references" material was among the most useful parts of the written record of the Expedition.
--John Logan Allen