Yridia II is mostly a water world. Only 1% consists of land above ocean level. The ocean contains a very diverse ecosystem. 10 million years ago, the fossil record indicates that three major continents existed above water when the climate was much cooler and more water was locked in ice caps. Since then, a warming trend has all but submerged these continents. Though there is no visible geological activity from space, plate tectonics still exist on Yridia II. It is therefore no surprise that geothermal heating is largely responsible for maintaining the underwater civilization on Yridia II. In the western hemisphere, there are two huge geologic features. One of these is a vast rift spanning 4500 kilometers in a roughly east-west direction. The second is more unusual still. Roughly 2000 kilometers from the last Yridian outpost exists a large subterranean system of caves away from the fault lines and subduction between tectonic plates further to the east. The area was recently discovered, is believed to be stable, and is not connected to the ocean.