Daily flights will operate between Pittsburgh and the Californian cities using Airbus 319 aircraft.
Greg Kaldahl, the airline’s vice president of resource planning, said that the new routes will ensure that people living in Pittsburgh "have a convenient, daily service across the country and one-stop connections to Asia".
"With United now providing services between Pittsburgh and all five of our hubs across the US, our customers have numerous options for the best service that gets them where they need to go."
United Airlines currently operates 32 flights a day to and from Pittsburgh and Chicago, Denver, Los Angeles, San Francisco and Washington DC.
The airline flies to more than 200 domestic and international destinations and has hubs at Denver, Chicago and Washington DC as well as the west coast cities.
Earlier this month, United launched a carbon offset programme that allows its customers to support renewable energy and reforestation schemes.