This is the only timeline in which the Crucible exists.
Ultimate Ben Timeline
In this timeline, Ben refused to give up the Ultimatrix. As a compromise, Azmuth agreed to combine it with the improved Omnitrix system.
This is also the timeline in which The Last Days of Bivalvan takes place, and therefore is the home dimension of Time Breaker Bivalvan.
Eon's original timeline, this universe is cold and desolate. It is with neither time nor purpose. Also referred to as Eon's Dimension.
The timeline in which the Eon Crisis took place. It is said to be the only timeline in which Ben Tennyson NEVER learns of the Omnitrix in any capacity, though this was obviously no longer true after the Eon Crisis. No Watch, No Problem! also takes place in this timeline.
A dimension in which a series of wars led to the evaporation of all surface water on Earth. As a result, society is in ruin and only the strong can rule. Mad Ben comes from this dimension, once ruling his own encampment. However thanks to Ben 10 and Ben 23, he was overthrown and his access to his Omnitrix removed.
Gwen 10's Dimension
A dimension were Gwen received the Omnitrix instead of Ben. It is home to Gwen 10, and eventually Gwen 10'000.