"The cache being completed, I walked to it and examined its construction. It is in a high plain about 40 yards distant from a steep bluff of the south branch on its northern side The situation a dry one, which is always necessary. A place being fixed on for a cache, a circle about 20 inches in diameter is first described, the turf or sod of this circle is carefully removed, being taken out as entire as possible in order that it may be replaced in the same situation when the cache is filled and secured. This circular hole is then sunk perpendicularly to the depth of one foot, if the ground be not firm, somewhat deeper. They then begin to work it out wider as they proceed downward, until they get it about six or seven feet deep, giving it nearly the shape of a kettle, or lower part of a large still. Its bottom is also somewhat sunk in the center.
The dimensions of the cache are in proportion to the quantity of articles intended to be deposited. As the earth is dug, it is handed up in a vessel and carefully laid on a skin or cloth, and then carried to some place where it can be thrown in such manner as to conceal it, usually into some running stream where it is washed away and leaves no traces which might lead to the discovery of the cache.
Before the goods are deposited, they must be well dried. A parcel of small dry sticks are then collected, and with them a floor is made, three or four inches thick, which is then covered with some dry hay or a raw hide well dried. On this, the articles are deposited, taking care to keep them from touching the walls by putting other dry sticks between as you stow away the merchandise. When nearly full, the goods are covered with a skin, and earth thrown in and well rammed until, with the addition of the turf first removed, the hole is on a level with the surface of the ground. In this manner, dried skins or merchandise will keep perfectly sound for several years."
Captain Meriwether Lewis, 9 June 1805