A still nameless ridge of mountains, rising to heights of over 20,000 feet, extends east from the Himalayas and separates Tibet from the headwaters of the Irrawaddy river. For more than two months each winter, temperatures fall well below freezing and fierce storms envelop the region in snow. Between the mountains, narrow and thickly forested valleys are crowded with rhododendrons, magnolias, maples, firs and tall Formosan pines, and the mountains themselves, in their lower reaches, are covered in dwarf junipers and an abundance of small evergreens and perennials.

Here, in this home of tigers, Himalayan black bears and the Asian rhinoceros, two small rivers, the Mali Hka and the N'Mai Hka, have their origin. Fed by the melting snows, they wind their way south and eventually merge to form the Irrawaddy just below the twenty-sixth parallel. From this confluence, the river rushes down, in occasionally violent torrents, through steep gorges, some only fifty yards across, before reaching the hot arid plains below.

The country which it crosses through nearly all of its 700-mile-long journey to the sea is very dry, with cool winters and scorching summers, a dusty expanse of alluvial land where temperatures climb to an average of over 100 degrees Fahrenheit in March and April and the annual precipitation in places barely reaches twenty inches. The rains, when they do come, come in a few sharp downpours, violent monsoon storms which transform waterless stream beds into dark brown torrents in a matter of minutes. Much of the region is covered in a dry scrub forest of short thorny acacias, euphorbia and cutch.