Dungeon Master's Guide

At the other end of the plane. near the Frostfell (the
plane of ice that borders the Plane of Water), is a region
of frigid winds called the Mistral Reach. These gales
drive snowstorms into the Frostfell and away from it,
.toward the heart of the plane. Earth motes in the reach
are covered with snow and ice.
I
PLANE OF EARTH
Earth symbolizes stability, rigidity, stern resolve, and
tradition. The plane's position opposite the Plane of
Air in the ring of the Elemental Planes reflects its
opposition to almost everything air represents.
The Plane of Earth is a chain of mountains rising
higher than any mountain range in the Material Plane.
It has no sun of its own, and no air surrounds the peaks
of its highest mountains. Most visitors to the plane
arrive by way of caves and caverns that honeycomb the
mountains.
The largest cavern beneath the mountains, called
the Great Dismal Delve or the Sevenfold Mazework, is
home to the capital city of the dao, the City of jewels.
The dao take great pride in their wealth and send teams
of slaves across the plane in search of new veins of
ore and gemstones to exploit. Thanks to their efforts,
every building and significant object in the city is made
from precious stones and metals, including the slender
gemstone-inlaid spires that top most buildings. The city
is protected by a powerful spell that alerts the entire dao
population if a visitor steals even a single stone. Theft is
punishable by death, with punishment extending to the
thief's relatives.
The mountains nearest the Fountains of Creation (on
the Plane of Fire) are called the Furnaces. Lava seeps
through their caverns, and the air reeks of sulfur. The
dao have great forges and smelting furnaces here to
process their ores and shape their precious metals.
The border region between the planes of Water and
Earth is a horrid swamp where twisted, gnarled trees
and thick, stinging vines grow from the dense muck and
slime. Here and there within the Swamp of Oblivion
(also called the Plane of Ooze), stagnant lakes and pools
play host to thickets of weeds and monstrous swarms of
mosquitoes. The few settlements here consist of wooden
structures suspended above the muck. Most are built on
platforms between trees, but a few stand on stilts driven
deep into the muck. No solid earth underlies the mud
of the swamp, so houses built on poles eventually sink
down into it.
It is said that any object cast into the Swamp of
Oblivion can't be found again for at least a century. Now
and then, a desperate soul casts an artifact of power into
this place, removing it from the multiverse for a time.
The promise of powerful magic lures adventurers to
brave the monstrous insects and hags of the swamp in
search of these treasures.
The region of the plane nearest the Swamp of
Oblivion is called the Mud Hills. Landslides constantly
wear away the slopes of the hills, sending cascades
of earth and stone into the bottomless swamp. The
Plane of Earth seems to constantly regenerate the land,
pushing new hills up as the old ones erode to nothing.