Why did Lewis and Clark take different routes on the return from the pacific?

The explorers began their journey home on March 23, 1806. On July 3, after crossing the Continental Divide, the Corps split into two teams so Lewis could explore the Marias River. Lewis and Clark stayed separated until they reached the confluence of the Yellowstone and Missouri Rivers on August 11. Once reunited, the Corps was able to return home quickly via the Missouri River. They reached St. Louis on September 23, 1806.