Mahakam Ulu, an ancient watershed in East Kalimantan, Indonesia, offers a glimpse into what Borneo used to be — before demand for coal, potato chips, shrimp, and even RVs wiped out about a third of the island’s rainforest. Slightly smaller than the state of South Carolina, the region teems with iconic and strange life: Proboscis monkeys, clouded leopards, Bornean orangutans — stouter and more reddish-brown than their Sumatran cousins — and Irrawaddy river dolphins.