Complex sentence: When work on the Santa Fe Trail ended in 1827, the Sibleys returned to St. Charles, Missouri's first capitol early in it's statehood and where Mary's father, Rufus Easton, was the second Attorney General for the State.
Split into simpler sentences: When work on the Santa Fe Trail ended, the Sibleys decided to move to St. Charles, Missouri in 1827. Early in Missouri's statehood (which in 1821 established its first capitol in St. Charles), Mary's father, Rufus Easton, was the second Attorney General for the State.