March 18

1868 South Pass City Post Office, named for the historic South Pass, was established for a second time on March 18, 1868. It was originally established in 1861 when the area was part of Nebraska Territory. South Pass City was named the county seat of Carter County when it was established in 1867. It remained the county seat even after Carter County was renamed Sweetwater County in 1869. In 1873, Green River City was named the county seat of Sweetwater County. Today, South Pass City is a Wyoming historic site. For more information visit this link.

1994 The triceratops was adopted as the State Dinosaur of Wyoming on March 18, 1994.