The only way to access this "Martian Haven" was via a heavily defended Martian Embassy; even then, only those with Martian DNA were allowed to proceed to the city beyond.
As the JFO arrived in their new home, they detected the presence of this universe's Martian Empire - dormant, but still present. Fearing an obstacle to their continued existence and rise to power, they killed Linda's boyfriend, David, and framed the Martians for the deed.
Incensed, Linda stormed the Embassy in search of a Martian Resurrection Chamber, but was killed by the JFO in the process. Shortly after her resurrection, she was manipulated into using the Power Booster Rod to wipe out all Martians remaining on Earth, including the colonists.
The Embassy remained undisturbed until the Head Alien rediscovered its location using the Sensitive Scanner. His activities attracted the attentions of SEMME, who dispatched several Squadrons to secure the area. All this played into the Head Alien's plans: with SEMME on-site, he could use their Martian DNA to gain access to the colony beyond. However, he found himself on the wrong end of some falling resurrection chambers and was killed along with SEMME's Big Boss, Anthony McHenry.
The Embassy's systems later revived the Head Alien. Now imbued with Martian DNA, was able to take control of the Embassy's various technologies and launch an attack on Denver. Less than pleased with this abuse, The Cheese destroyed the Martian Embassy.