Final answer:
The primary gemstone mined in the Peninsular Ranges is garnet, which is found in the metamorphic rocks of these mountain ranges.
Step-by-step explanation:
The primary gemstone mined in the Peninsular Ranges is not diamond, ruby, or emerald; the correct answer is D) Garnet. The Peninsular Ranges are a group of mountain ranges in the Pacific Coast Ranges, which span from Southern California to Baja California in Mexico. Garnets are silicate minerals that come in various colors and are frequently found in metamorphic rocks, which are abundant in the Peninsular Ranges.