Final answer:
China's southwestern border is marked by the Himalayan Mountains, which serve as a natural boundary between China and India.
Step-by-step explanation:
The geographical feature located on China's southwestern border is the Himalayan Mountains. This majestic mountain range acts as a natural boundary between China and India. The Himalayas are significant both in their grand physical presence and as a feature that has influenced political boundaries and human activities in the region. Notably, the Himalayas serve as one of the most recognizable geographic features separating South Asia and East Asia.