Question: Where is the origin of the river that Orlam clans crossed to migrate to Namibia?

Context paragraphs:
paragraph_text: The Cả River (Laotian: Nam Khan, Vietnamese: Sông Cả or better known as sông Lam or Lam River wikt:蓝) is a river in mainland Southeast Asia. It originates in the Loi Mountains of Laos, crossing Laos's Xiangkhouang Province, Vietnam's Nghệ An and Hà Tĩnh provinces and empties into the Gulf of Tonkin, on the North Central Coast of Vietnam, after a 512 km journey. The Cả River zone is classified as 300 km by the Vietnam Geographical Survey. The Bến Thủy bridge, crossing into Bến Thủy, Vinh, crosses the Cả River on its Cửa Hội estuary.
title: Cả River
paragraph_text: The Severn Bridge () is a motorway suspension bridge operated by Highways England that spans the River Severn and River Wye between Aust, South Gloucestershire in England, and Chepstow, Monmouthshire in South East Wales, via Beachley, Gloucestershire, which is a peninsula between the two rivers. It is the original Severn road crossing between England and Wales, and took three-and-a-half years to construct at a cost of £8 million. It replaced the Aust Ferry.
title: Severn Bridge
paragraph_text: Namibia (i/nəˈmɪbiə/, /næˈ-/), officially the Republic of Namibia (German:  Republik Namibia (help·info); Afrikaans: Republiek van Namibië) is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and east. Although it does not border Zimbabwe, a part of less than 200 metres of the Zambezi River (essentially a small bulge in Botswana to achieve a Botswana/Zambia micro-border) separates it from that country. Namibia gained independence from South Africa on 21 March 1990, following the Namibian War of Independence. Its capital and largest city is Windhoek, and it is a member state of the United Nations (UN), the Southern African Development Community (SADC), the African Union (AU), and the Commonwealth of Nations.
title: Namibia
paragraph_text: The Zulu were originally a major clan in what is today Northern KwaZulu - Natal, founded ca. 1709 by Zulu kaMalandela. In the Nguni languages, iZulu means heaven, or weather. At that time, the area was occupied by many large Nguni communities and clans (also called isizwe = nation, people or isibongo = clan or family name). Nguni communities had migrated down Africa's east coast over centuries, as part of the Bantu migrations probably arriving in what is now South Africa in about the 9th century.
title: Zulu people
paragraph_text: The Omaruru River is a major river crossing the Erongo Region of western central Namibia from East to West. It originates in the Etjo mountains, crosses the city of Omaruru and reaches the sea a few kilometers north of Henties Bay.
title: Omaruru River
paragraph_text: The comune takes its name from the Rubicon, famous for Julius Caesar's historic crossing. A combination of natural and man-made changes caused the original Rubicon to change course repeatedly since then. For centuries the exact location of the original river was unknown. In 1991, the Fiumicino, a river which crosses Savignano sul Rubicone, was identified as the most likely location for the original Rubicon. Prior to that the region was called Savignano di Romagna.
title: Savignano sul Rubicone
paragraph_text: Originally the Emperor and non-warrior nobility employed these warrior nobles. In time, they amassed enough manpower, resources and political backing in the form of alliances with one another, to establish the first samurai-dominated government. As the power of these regional clans grew, their chief was typically a distant relative of the Emperor and a lesser member of either the Fujiwara, Minamoto, or Taira clans. Though originally sent to provincial areas for a fixed four-year term as a magistrate, the toryo declined to return to the capital when their terms ended, and their sons inherited their positions and continued to lead the clans in putting down rebellions throughout Japan during the middle- and later-Heian period. Because of their rising military and economic power, the warriors ultimately became a new force in the politics of the court. Their involvement in the Hōgen in the late Heian period consolidated their power, and finally pitted the rival Minamoto and Taira clans against each other in the Heiji Rebellion of 1160.
title: Samurai
paragraph_text: Princes Bridge, originally Prince's Bridge, is a bridge in central Melbourne, Australia that spans the Yarra River. It is built on the site of one of the oldest river crossings in Australia. The bridge connects Swanston Street on the north bank of the Yarra River to St Kilda Road on the south bank, and carries road, tram and pedestrian traffic. The present bridge was built in 1888 and is listed on the Victorian Heritage Register.
title: Princes Bridge
paragraph_text: Meat Corporation of Namibia, locally known as MeatCo, is a meat processing company headquartered in Windhoek, the capital of Namibia. It is the largest exporter of prime beef in Namibia.
title: Meat Corporation of Namibia
paragraph_text: The river Khan is an ephemeral river crossing the Erongo region of central Namibia. It is the main tributary of the Swakop River and only occasionally carries surface water during the rain seasons in November and February/March.
title: Khan River
paragraph_text: Orange Gariep, Oranje, Senqu River Sunset over the Orange River near Upington in the Northern Cape Countries Lesotho, South Africa, Namibia Tributaries - right Caledon River, Vaal River, Fish River (Namibia) Landmarks Gariep Dam, Augrabies Falls Source Thaba Putsoa - location Maloti Mountains (Drakensberg), Lesotho - elevation 3,350 m (10,991 ft) Mouth Alexander Bay - location Atlantic Ocean Length 2,200 km (1,367 mi) Basin 973,000 km (375,677 sq mi) Discharge - average 365 m / s (12,890 cu ft / s) The course and watershed of the Orange River, Caledon River and Vaal River. This map shows a conservative border for the watershed. Specifically, the Kalahari basin is excluded, as some sources say it is endorheic. Some other sources using computational methods show a basin which includes parts of Botswana (and hence of the Kalahari).
title: Orange River
paragraph_text: The Calabar River in Cross River State, Nigeria flows from the north past the city of Calabar, joining the larger Cross River about to the south. The river at Calabar forms a natural harbor deep enough for vessels with a draft of .
title: Calabar River
paragraph_text: The Migration Series, originally titled The Migration of the Negro, is a group of paintings by African-American painter Jacob Lawrence which depicts the migration of African Americans to the northern United States from the South that began in the 1910s. It was published in 1941 and funded by the WPA.
title: Migration Series
paragraph_text: The area is crossed by the N6 road, of the Route Nationale and is bordered to the north by the Mangala river and to the south by the Congo River.
title: Lisala
paragraph_text: The dry lands of Namibia were inhabited since early times by San, Damara, Nama and, since about the 14th century AD, by immigrating Bantu who came with the Bantu expansion from central Africa. From the late 18th century onwards, Orlam clans from the Cape Colony crossed the Orange River and moved into the area that today is southern Namibia. Their encounters with the nomadic Nama tribes were largely peaceful. The missionaries accompanying the Orlams were well received by them, the right to use waterholes and grazing was granted against an annual payment. On their way further northwards, however, the Orlams encountered clans of the Herero tribe at Windhoek, Gobabis, and Okahandja which were less accommodating. The Nama-Herero War broke out in 1880, with hostilities ebbing only when Imperial Germany deployed troops to the contested places and cemented the status quo between Nama, Orlams, and Herero.
title: Namibia
paragraph_text: Namibia's primary tourism related governing body, the Namibia Tourism Board (NTB), was established by an Act of Parliament: the Namibia Tourism Board Act, 2000 (Act 21 of 2000). Its primary objectives are to regulate the tourism industry and to market Namibia as a tourist destination. There are also a number of trade associations that represent the tourism sector in Namibia, such as the Federation of Namibia Tourism Associations (the umbrella body for all tourism associations in Namibia), the Hospitality Association of Namibia, the Association of Namibian Travel Agents, Car Rental Association of Namibia and the Tour and Safari Association of Namibia.
title: Namibia
paragraph_text: The Molopo River () is one of the main rivers in Southern Africa. It has a length of approximately 960 kilometres and a catchment area of 367,201 km with Botswana, Namibia and South Africa sharing roughly about a third of the basin each.
title: Molopo River
paragraph_text: Pelly Crossing is a community in Yukon, Canada. It lies where the Klondike Highway crosses the Pelly River. Population in 2008 was 291.
title: Pelly Crossing
paragraph_text: Jonker Afrikaner ( 1785, "Roode Zand" near Tulbagh, South Africa – 18 August 1861, Okahandja, South West Africa) was the fourth Captain of the Orlam in South West Africa, succeeding his father, Jager Afrikaner, in 1823. Soon after becoming "Kaptein", he left his father’s settlement at Blydeverwacht with three brothers and some 300 followers and relocated to the area that is today central Namibia. From 1825 onwards he and his council played a dominant political role in Damaraland and Namaland, creating a "de facto" state.
title: Jonker Afrikaner
paragraph_text: The Mayuni Conservancy is a conservation area in Linyanti Constituency, in Namibia's northeastern Caprivi Region, along the eastern bank of the Cuando River.
title: Mayuni Conservancy

Reasoning steps:
Orlam clans crossed which river to migrate to Namibia? >>>> Orange River
where is the origin of Orange River >>>> Thaba Putsoa

Answer: spans: Thaba Putsoa