From ErfWiki

Proposed Canon

Spacerock is the capital city of Jetstone.

Speculation

Being the capital of a very powerful side, Spacerock is probably a level 5 city.

Real World References

The name of the faction, Jetstone, seems to be a portmanteau of the names of the Hanna-Barbera cartoons The Jetsons and The Flintstones. The capital, Spacerock, is named according to the themes on the two shows. It might be meant as a portmanteau of something starting with "Space" and Bedrock, the city the Flintstones live in.