Question: What is the height of the tallest mountain from which the Glen River flows?

Context:
Agri (river)
The Agri is a river in the Basilicata region of southern Italy.
 In ancient times it was known as "Aciris" (Ancient greek: "Akyris", "Ακυρης").
 The source of the river is in the Lucan Apennines north of Monte Volturino and west of Calvello in the province of Potenza.
 It is near the source of the Basento.
 The river flows south near Paterno before curving southeast.
 It flows near Tramutola, Viggiano, and Grumento Nova before entering a lake.
 After exiting the lake, the river flows eastward near Armento, Missanello, Aliano, and Sant'Arcangelo.
 A right tributary, the Racanello, enters the river in this area.
 The river forms the border between the province of Potenza and the province of Matera for part of this area of the river.
 It flows into a small lake before entering the province of Matera.
 The river flows for a short distance before entering Lago di Gannano.
 After exiting the lake, the river flows southeast near Tursi, Montalbano Jonico, and Scanzano Jonico before flowing into the Gulf of Taranto near Policoro.
List of tallest mountains in the Solar System
This is a list of the tallest mountains in the Solar System.
 The tallest peak or peaks on worlds where significant mountains have been measured are given; in some cases, the tallest peaks of different classes on a world are also listed.
 At 21.9 km, the enormous shield volcano Olympus Mons on Mars is the tallest mountain on any planet.
 For 40 years, following its discovery in 1971, it was the tallest mountain known in the Solar System.
 However, in 2011, the central peak of the crater Rheasilvia on the asteroid and protoplanet Vesta was found to be of comparable height.
Donard Forest
Donard Forest is located near Newcastle, County Down, Northern Ireland.
 It borders Donard Park at the foot of the Mourne Mountains.
 The Glen River flows through the forest where it is crossed by three stone bridges.
 The north east section of the forest contains a Heritage Stand of Scots and Corsican pine planted in 1927.
 A south east section, beside the Glen River, was the former site if Donard Lodge.
 The lodge was built in the 1830s by the Annesley family and demolished in 1966 after falling into ruin.
 The Annesleys planted a number of exotic trees in the area surrounding the house, including Giant Redwoods and Monkey Puzzles.
 There is also a small stone shelter, built in 1842, a short distance from the river.
List of tallest dams in China
The tallest dams in China are some of the tallest dams in the world.
 Nearly 22,000 dams over 15 m in height – about half the world's total – have been constructed in China since the 1950s.
 Many of the tallest are located in the southwestern part of the country (Guizhou, Sichuan, Yunnan) on rivers such as the Mekong, the Yangtze, and its upper stretch (Jinsha River) and tributaries (Yalong, Dadu, Min and Wu).
 The Yellow River in the western part of the country also hosts several among the tallest.
 Purposes for these high structures include flood control, irrigation and, predominantly, hydroelectric power.
 While beneficial, many throughout the country have been criticized for their effects on the environment, displacement of locals and effect on transboundary river flows.
 Currently, the country's and world's tallest, Jinping-I Dam, an arch dam 305 m high, is located in Sichuan.
 The tallest embankment dam in China is the 261 m Nuozhadu Dam in Yunnan.
 The country's highest gravity dam is Longtan Dam at 216.2 m , which can be found in Guangxi.
 At 233 m , Shuibuya Dam in Hubei is the world's tallest concrete-face rock-fill dam.
 In Sichuan, the government is constructing the 312 m tall Shuangjiangkou Dam which, when complete, will become the world's tallest dam.
Marecchia
The Marecchia (pronounced ] ) is a river in eastern Italy.
 In ancient times it was known as the "Ariminus" which was from the Greek "Ariminos", "Αρίμινος" (which is also the ancient name of Rimini).
 The source of the river is near Monte dei Frati which is east of Pieve Santo Stefano and southwest of Badia Tedalda in the province of Arezzo in Tuscany.
 It flows northeast into the province of Pesaro and Urbino in the Marche and is the only river that runs through Montefeltro.
 While flowing through Montefeltro, the river flows through the exclave Santa Sofia Marecchia, which belongs to Badia Tedalda.
 The river then flows past Sant'Agata Feltria and Novafeltria before crossing into the province of Rimini in Emilia–Romagna.
 At Torello, part of the commune of San Leo, it flows 1 km west of the Sammarinese territory Acquaviva and the San Marino River flows into it, but the Marecchia does not touch the San Marino border.
 Finally, the river flows past Verucchio and Santarcangelo di Romagna before flowing into the Adriatic Sea near Rimini.
Wheeler Peak Glacier
Wheeler Peak Glacier is a glacier situated at the base of Wheeler Peak within Great Basin National Park in the U.S. state of Nevada.
 It has been called the southernmost glacier in the Northern Hemisphere but is much further north than Mount Everest and glaciers of the Himalaya and also further north than Palisade Glacier in California.
 At a height of 13063 ft Wheeler Peak is the tallest mountain in the Snake Range and the second tallest mountain in Nevada.
 The mountain top is also considered to be a horn, a peak carved and shaped by glaciers over a long period of time.
Mourne Mountains
The Mourne Mountains ( ; Irish: "na Beanna Boirche" ), also called the Mournes or Mountains of Mourne, are a granite mountain range in County Down in the south-east of Northern Ireland.
 It includes the highest mountains in Northern Ireland and the province of Ulster.
 The highest of these is Slieve Donard at 850 m .
 The Mournes is an Area of Outstanding Natural Beauty and has been proposed as the first national park in Northern Ireland.
 The area is partly owned by the National Trust and sees a large number of visitors every year.
 The name "Mourne" (historically spelt "Morne") is derived from the name of a Gaelic clann or sept called the "Múghdhorna".
Bidente-Ronco
The Bidente-Ronco is a river in the Emilia-Romagna region of Italy.
 The first portion of the river is called the Bidente.
 Once the river passes under the Ponte dei Veneziani (Bridge of the Venetians) in Meldola, the river is called the Ronco.
 The source of the river is near the border between the province of Forlì-Cesena, the province of Arezzo, and the province of Florence in the Foreste Casentinesi, Monte Falterona, Campigna National Park.
 The river flows northeast through the mountains in the province of Forlì-Cesena and flows near Santa Sofia, Galeata, Civitella di Romagna and Meldola.
 Beyond Meldola, the river flows north near Bertinoro, Forlimpopoli, and Forlì before crossing the border into the province of Ravenna.
 The river flows northeast until it joins the Montone south of Ravenna, and the resulting river is known as the Uniti.
 The Battle of Ronco took place here.
Glen River, County Down
Glen River is a short river in County Down, Northern Ireland.
 The two mile course flows north east from the foot of Slieve Commedagh and Slieve Donard in the Mourne Mountains into Dundrum Bay at Newcastle, descending 1,500 ft .
Jirisan
Jirisan is a mountain located in the southern region of South Korea.
 It is the second-tallest mountain in South Korea after Jeju Island's Hallasan, and the tallest mountain in mainland South Korea.
 After Jirisan, Seoraksan is the third tallest mountain in South Korea and the second-tallest mountain on the South Korean mainland.

Answer: 850 m