Hajar Mountains

The Hajar Mountains are one of the highest mountain ranges in the Arabian Peninsula, shared between northern Oman and eastern United Arab Emirates. Also known as "Oman Mountains", they separate the low coastal plain of Oman from the high desert plateau, and lie 50–100 km inland from the Gulf of Oman.

Al means "the", and Ḥajar means "stone" or "rock". So al-Ḥajar is named as "the stone" or "the rock".

Source: Wikipedia