The Gehenna System is very old, lying close to the galatic core in the sector of the galaxy known as the Ultima Segmentum. It seems that out of the seventeen planetoids in the Gehenna System only one, Gehenna Prime, was terraformed and colonised long ago in the first expansion of mankind. Gehenna Prime is slightly larger than Earth and exhibits a faster rotation. This gives rise to increased vulcanism and a bult of active and semi-active volcanoes around the planet's equator known as the Graildark mountains. The volcanoes give onto jungle highlands and extinct volcanic chains which eventually peter out into broad plains to the north and south of the equator.
The mile high termite towers of mankin's hives sprawl over the plains. Yhe lie in the midst of carefully cultivated croplands covered over by armourglass and plasteel. The weather on Gehenna can become spectacular at times as the coriolis storms born in the Graildark mountains sweep down onto the plains with astonishing force. During these dangerous storms all living creatures in the mountains must take shelter from the winds or be torn appart. On the plains things are a little easier but the storms can still be deadly at times and the powerful lightning strikes associated with them can wreak havic with electrical systems.
However, in comparision to many Imperial Worlds Gehenna is an unspoilt wilderness of mountains and plains. This is because the wealth of Gehenna comes not from the great industrial sectors pumping out noxious waste, nor from kilometers long factory ships gulping down its oceanic lifeforms, nor from mass havesting of rigidly controlled grasses, cereals or other crops. Gehenna's value to the Imperium lies in its equatorial crystal mines(Cross Ref. Adaptus Mech. Files X21/23.19/phase crystal systems).
The Mountains are riddled with twisting, labyrinthe mine shafts which turn and loop to avoid the active lava tubes. No large scale strip mining is possible because of the vulcanism and seismic upheaval. Men must creep, in breathmasks and coldsuits, through the shaking roots of the mountains to seek the crystals. The crystals can be seeded and 'grown' artficialy in orbital factories, and are used to manufacture lasers and powerstacks for the weapons and machines of the Adaptus Mechanicus.
Reproduced from The Fires of Gehenna scenarios booklet. Used without permission.