The first successful United States Pony Express run from St. Joseph, Missouri, to Sacramento, California, begins.

The Pony Express was an American express mail service that used relays of horse-mounted riders between Missouri and California. It was operated by the Central Overland California and Pikes Peak Express Company.

St. Joseph is a city mostly in and county seat of Buchanan County, Missouri, United States. A small portion of the city extends north into Andrew County. Located on the Missouri River, it is the principal city of the St. Joseph Metropolitan Statistical Area, which includes Buchanan, Andrew, and DeKalb counties in Missouri and Doniphan County, Kansas. As of the 2020 census, St. Joseph had a total population of 72,473, making it the 8th most populous city in the state, and the 3rd most populous in Northwest Missouri. St. Joseph is located roughly thirty miles north of the Kansas City, Missouri, city limits and approximately 125 miles (201 km) south of Omaha, Nebraska.

Sacramento is the capital city of the U.S. state of California. The county seat of Sacramento County, it is located at the confluence of the Sacramento and American Rivers in the Sacramento Valley. It is the fourth-most populous city in Northern California, sixth-most populous in the state, and 35th-most populous city in the United States with a population of 524,943 at the 2020 census, while the Sacramento metropolitan area with 2.46 million residents is the 27th-largest metropolitan area in the nation.

April 3 is the 93rd day of the year in the Gregorian calendar; 272 days remain until the end of the year.