The Andelain hills are one of the last remnants of the One Forest and home to the Wraiths of Andelain. The Earthpower here is very strong, being at the center of the Land.
They are deemed the heart-healing richness of the Land. Evilness is felt faintly here by Thomas Covenant through the ground, according to Atiaran for it to be felt even here it has to be supremely great for the hills to not feel safe.
This evilness is shown later to be the Ur-Viles that come to attack the Wraiths of Andelain during the Dance of the Wraiths of Andelain.