Sierra de Lema

The Sierra de Lema is a mountainous upland area of Bolívar state, Venezuela. Lying north of the Gran Sabana, it marks the divide between the drainage basins of the Caroní and Cuyuni Rivers. It is partly within the bounds of Canaima National Park and encompasses a number of prominent tepuis, including the entire Los Testigos chain and Ptari Massif. The elevational range of the Sierra de Lema is around 150–1,650 metres (490–5,410 ft) above sea level. The names Sierra Rinocote and Sierra Usupamo (or Usupama Mountains) have historically been applied to its eastern and western portions, respectively.

The chain of mountains that comprises the Sierra de Lema is around 30 kilometres (19 mi) wide. Because the toponymy of the region remains largely unresolved, the stated length of the Sierra de Lema can vary widely, depending on the definition used. When considering only the uplands that mark the northern boundary of the Gran Sabana, the Sierra de Lema spans around 80 km (50 mi). But the extent of the range exceeds 200 km (120 mi) if the entire chain separating the Caroní and Cuyuni drainage basins is included. By the latter definition, the Sierra de Lema stretches from Cerro Venamo in the east to Serranía Supamo and Cerro Santa Rosa in the west (very close to the confluence of the Paragua and Caroní Rivers).

The old-growth forest of the Sierra de Lema remains virtually intact, covering a contiguous area of some 1,000 square kilometres (390 sq mi). It is characterised by nutrient poor soils with a low pH and high aluminium content. The El Mirador ("The Lookout") area at the base of the Sierra de Lema exhibits unusually high levels of the radioisotope Caesium-137, in both its soils and vegetation. This is likely related to the ground composition and cloud forest conditions of the site. The undulating, forested landscape of La Escalera ("The Staircase") also forms part of the Sierra de Lema.

The Sierra de Lema consists of an igneous-metamorphic basement overlain by Precambrian sedimentary rocks of the Roraima Group, with Mesozoic diabase intrusions.