"The United States had been on a de facto gold standard since the 1830s and de jure gold standard since 1900. In 1913 the gold standard was built into the framework of the Federal Reserve. The law required the Federal Reserve to hold gold equal to 40 percent of the value of the currency it issued (technically termed the Federal Reserve Note but colloquially called the dollar) and to convert those dollars into gold at a fixed price of $20.67 per ounce of pure gold."
Imho, this virtually guaranteed an eventual bank run. Only the fact that gold is inconvenient to transact in allowed the fed to get away with partial backing from 1913 to the eventual EO6102 confiscation order in 1933.