The Marungu highlands rise west of the southern half of Lake Tanganyika, in the Tanganyika Province of the Democratic Republic of the Congo. The range is split by the Mulobozi River, which empties into the lake just north of Moba port. The northern section reaches 2,100 meters; the larger southern section tops out at 2,460 meters. Average annual rainfall runs about 1,200 millimeters, mostly falling between October and April. The soils are relatively nutrient-poor, which sets limits on what agriculture the highlands can sustain. Most of the higher slopes are Miombo woodland savanna. On the slopes are scrub plants, and in the ravines a richer forest survives - dense in places, with riparian forest running along the streams. This is the mosaic that makes the Marungu a refuge for species that would not survive out on the open plateau.

Under Lake Tanganyika's southern basin runs a ridge - a sublacustrine swell that extends from the Marungu plateau itself and divides the southern lake into the Albertville and Zongwe basins. The Zongwe trough holds the deepest part of the lake, 1,470 meters below present surface level. Alluvial cones from rivers that drain the Marungu sit at the foot of the Zongwe trough. Many V-shaped valleys run under the current lake level. These are the fingerprints of a radically different past. Over the Quaternary - the last 2.588 million years - the lake level has varied dramatically; at times the lake was far lower than now, and what is underwater today was dry plateau cut by actual rivers. Stanley noticed this when he visited the region on his 1874-1877 crossing of Africa. He wrote that Kirungwe Point 'appears to be a lofty swelling ridge, cut straight through to an unknown depth,' and guessed that it had once been a prolongation of the Marungu plateau, the rocks on both sides of the lake identical. He was reading the evidence correctly 150 years ago.

The list of what lives in the Marungu ravines reads like a botanical roll call of high central Africa. Parinari excelsa, Teclea nobilis, Polyscias fulva, Ficus storthophylla, and Turrea holstii grow in ravines. By the streams you find Syzygium cordatum, Ficalhoa laurifolia, and Ilex mitis. Many of these are trees you could encounter across east and central African montane forests - but the community they form here, at this altitude, in this specific climate, is not replicated elsewhere in exactly this arrangement. Then there is Hyperolius nasicus, a tree frog known only from Kasiki at 2,300 meters - a poorly studied member of the controversial Hyperolius nasutus group. And Prigogine's sunbird (Cinnyris prigoginei), a bird you will not see anywhere else on the planet. A 1990 assessment considered it one of 25 bird species in then-Zaire (out of 1,086 total) that were threatened. The riparian forest patches that hold the sunbird are small and vulnerable - logging and cattle-driven streambank erosion erode them further each year. Conservation proposals have suggested nature preserves above 1,500 meters on the Mulobozi and Lufuko rivers. No reserve system has yet taken hold.

Stone tools found in the Marungu date from the Early Pleistocene - over 780,000 years ago - through the present. The climate has alternated several times between arid and pluvial over that span. Human history here is deep. Richard Francis Burton, the English explorer, visited between 1857 and 1859. At that time, Marungu was a source region for enslaved people captured and marched to the great slave market at Ujiji on Lake Tanganyika's eastern shore. An Omani merchant who had lived in the region for five months told Burton it was divided into three provinces: Marungu to the north, Karungu in the center, Urungu in the south. Burton suspected 'Marungu' was originally the name of a people rather than a country - a reminder that nineteenth-century European cartographers often confused language groups with territories. The region had suffered raids from the Watuta, who had nearly wiped out the cattle of the inhabitants before Burton arrived. The enslavement of people and the destruction of cattle had left Marungu depopulated in places and precarious everywhere. It was into that wounded landscape that Stanley, then Thomson, would walk.

Stanley arrived in 1876 and wrote that, 'Though the mountains of Marungu are steep, rugged, and craggy, the district is surprisingly populous.' From the chasms, he could see other high mountains 2,500 feet above the lake, their summits occupied by villages whose inhabitants, he wrote, were 'evidently harassed by some more powerful tribes to the westward.' People had moved to inaccessible places for survival. Joseph Thomson came between 1878 and 1880 and found that Marunga had no head chief; it was divided into three independent chieftainships that sometimes fought one another. The chiefs were named Manda, Songwe, and Kapampa. Thomson had trouble getting permission to travel, and he did not enjoy the terrain. 'We had now no gentle undulations and rounded valleys,' he wrote, 'but savage peaks and precipices, alternating with deep gloomy ravines and glens. Ridge after ridge had to be crossed, rising with precipitous sides, and requiring hands and knees in the ascent.' But he also admitted the beauty: the sun darting rays through overhanging cloud, a peak crowned in gold, glimpses of Lake Tanganyika 2,000 feet below 'as calm and undisturbed as the sleep of innocence.' That view is still there. The Marungu is still there. And somewhere up in the ravines, a small pointed-snout frog is still holding on.