After SKYNET leveled the world in 2009, it began a conservative, if rapid, buildup of its industrial might._ SKYNET had been careful to intercept (and thus spare) the larger facilities that had been instrumental in its own construction from the retaliation strike from Russia and the token strike from China._ Even as the radioactive fallout from the strikes was settling across the American mainland, SKYNET was already mobilizing its plans._ In 2015 AJD(After Judgement Day), SKYNET consolidated its resources and manufacturing facilities in one area, a portion of the mid-Western United States which became known as Sector Zero._ Within Sector Zero, SKYNET ruled supreme and with total authority._ Huge, multi-level automated manufacturing complexes and industrial centers rose into the sky and nuzzled into the depths of the Earth._ All of the facilities were connected by a variety of cargo and unit mass transport systems, all were linked to several computer core systems, which were in turn interfaced to SKYNET directly.
SKYNET's automated mining systems began to filter out the planet's minerals, going farther and faster than any previous human attempts._ One such project became known to the humans as 'the Devil's Navel', and it was the first structurally sound deep core mine, fully automated, ten kilometers deep and increasing in depth by several hundred meters with each month._ When SKYNET found a thermal vein, it simply tapped into it and enjoyed new power for more production._ By 2020, Sector Zero was an impregnable fortress, a mechanical blemish on the surface of the Earth that could easily be seen from space, and it continued to grow every year._ By 2025, local resources had been depleted and except for the still sizeable outlay from the deep core mine, SKYNET began to expand to other areas of the country, setting up armored and armed fortresses, stationing units to both pacify the immediate area and then protect its mining interests._ SKYNET was greedy, but never wasteful._ it favored a short term, rapid depletion of immediate resources in order to exterminate the human race, followed by a protracted, perhaps centuries long, period of reclamation and recycling, a period where it would remake the Earth's surface over in its own image.
Benhacker
P.S. : See pic of on of Skynet's interior (Concept Art from the game Terminator 3 : Redemption)
They however probably will have survived longer than humans, much longer, due to more clever usage of the earths minerals, pumping their factories rather than ipods..