Mars Outpost is another colony on the planet Mars. It is in fact one of oldest colonies (older than Mars City) dating back to 2112.
It is divided into areas including the Entrance, Sectors 1-6, and the Reactor, etc. Which branch off of the center known as Junction.
It was largely cut off from Mars City and didn't hear all the details of the events on November 15, 2145. But it suffered its own incident, the Mars Incident, not long after.
The same Doom Marine (B.J. Blazkowicz) apparently stopped both incursions. The Marine had been dispatched apparently from Earth in response to a distress call from Union Aerospace Corporation's research facility on Mars. The base was under attack by an unknown force and his mission was to acquire intelligence and neutralize the threat. Once his insertion was complete ordered to rendezvou with the other Marines at Junction for further instructions. He was told to expect heavy resistance.