The northwestern section, named for reasons lost. "Kas" might have been a Riin leader, a spirit, or a word whose meaning died with the language. Lean D'Kas is less dense than Lean D'Riin, less obviously malevolent, but still not safe.
The Riin settled here more lightly—seasonal camps rather than permanent cities. The ruins are smaller, more scattered, easier to miss. This makes Lean D'Kas more dangerous in some ways: travelers don't realize they've crossed into forbidden territory until the forest starts responding.