Trivia Q #4: Mid-19th Century US Coin Circulation

SPQR actually is on track for the correct answer. By making the silver coins have lower silver content (1853) by weight, the practice for exporting them for more than face was squashed. This allowed those coins to finally circulate and compete against all the silver minor coins. Now, the Mint had a chance to finally get rid of all that foreign silver.

So the two major events that I was looking for (again maybe not all inclusive) are:
1 - January 24, 1848: The gold side of the equation was solved with Sutter's Mill and the California Gold Rush
2 - Coinage Act of 1853: The silver side of the equation; reduced weight of silver in minor coins to prevent exporting

The bi-metallic standard was still intact but, as always, on shakey ground until we went to the gold standard (and I forget off hand what year that was).

And, to be fair to SPQR, the Mint Act of 1853 is dated on the same calendar day as the Coinage Act of 1857.