The new project includes installing curbs and gutters along State Route 140.
Sidewalks and wheelchair ramps are also being added in front of businesses.
Pedestrian-activated warning lights are even being installed at intersections to alert drivers when people are crossing the road.
County leaders say it is important to maintain the historic look and feel of downtown Mariposa while completing the upgrades.
"We're working with Mariposa County on the historic style overhead lighting. They've actually purchased those fixtures, and Caltrans is installing them," said Bob Highfill, public information officer.
The pedestrian safety project began in May. It should be finished by the end of this year or early next year.