Beyond the mouth of the Dragonborn, there is not much current knowledge on Tel Tarkals planes. 
Hundreds of years ago, the Saurian inhabited the land and tamed countless native beasts, including great Wyverns and Dragons. In these times, Tel Tarkal was akin to a vast swampland but at it's abandonment, the lands shifted into an inferno. Raided by Dragons that spoke in a tongue none of the reptilians knew, as all possessed the ability to speak the ancient language, they could only assume the magic cast upon the beasts to be derived from the book of shadows. 

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Forced to abandon their lands, the Saurian people fled for safety in Elsgadir. Since, Dragons have stricken various locations excluding Notoria. Though travel is banned to Tel Tarkal, there are many foolish enough to set sail forth and all were certain to find a gruesome demise.