Well new facts behind the caches for Bearmouth, some finds were made but they date further back then the metal detector!
From 1905
FOUND IN THE MOUNTAINS
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Sack Stolen from Northern Pacific Train in the Month of October, 1893.
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Phillipsburg, Aug. 18─The registered mail pouch taken from the Northern Pacific train on the night of October 24, 1902, by an unknown train robber, has been found cached in a lonely spot in the mountains about five miles from Drummond, land about three miles northeast of the railroad. The discovery was made by a prospector named A.J. Howell. He reported the matter to Postmaster Featherton, at Drummond, and the latter went with him today to the spot where the pouch had been securely cached under a rock in the midst of a heap of boulders on the mountain top.
The pouch and contents, badly mutilated by mice and squirrels, was brought to Drummond, and the find reported to the United States authorities by wire. Every letter in the pouch had been opened, and all valuable contents extracted. It cannot be stated what the amount of booty secured was, but as far as can be ascertained at present, it was not large. The robbery of the Northern Pacific train on October 24, 1902, has never been fixed upon anyone; except that Christie has claimed that Hammond, who was his partner in the second holdup at Bearmouth, had confessed that it was his work.
It is said at Drummond that Hammond was working on a ranch near Ovando, in Powell county, both before and after the date of the first Bearmouth holdup, on October 24, 1902, and that the cache just discovered was on the route which would naturally be'taken by a man going from Bearmouith to Ovando by the most circuitous I way, and avoiding the well traveled roads. The contents of the pouch show conclusively that it was taken from the train at the time of the first holdup, The registered envelopes bear dates from October 20 to 23, and none have a later date than that last named.
The robber, whoever he was, chose an admirable spot in which to leisurely go through the pouch and its contents, as, from within the mass of boulders, a good view of every approach may be had. It is said that a man armed with a Winchester could, from a these natural defenses, have easily stood off 50 men.