Question: The Kingdom of Strathclyde is home to a medieval capital with a castle that sits on volcanic basalt that was how high?

Context paragraphs:
Touchet Formation: The Touchet Formation or Touchet beds consist of large quantities of gravel and fine sediment which overlay almost a thousand meters (several thousand feet) of volcanic basalt of the Columbia River Basalt Group in south-central Washington and north-central Oregon.  The beds consist of between 6 and 40 distinct rhythmites - horizontal layers of sediment, each clearly demarcated from the layer below.  These Touchet beds are often covered by windblown loess soils which were deposited later; the number of layers varies with location.  The beds vary in depth from 330 ft at lower elevations where a number of layers can be found to a few extremely thin layers at the maximum elevation where they are observed (1150 ft ).

Petroglyph National Monument: Petroglyph National Monument stretches 17 mi along Albuquerque, New Mexico's West Mesa, a volcanic basalt escarpment that dominates the city's western horizon.  Authorized June 27, 1990, the 7,236 acre (29.28 km) monument is cooperatively managed by the National Park Service and the City of Albuquerque.  The western boundary of the monument features a chain of dormant fissure volcanoes.  Beginning in the northwest corner, Butte volcano is followed to its south by Bond, Vulcan, Black and JA volcanoes.

Kingdom of Strathclyde: Strathclyde (lit. " Strath of the River Clyde"), originally Cumbric: Ystrad Clud or Alclud (and Strath-Clota in Anglo-Saxon), was one of the early medieval kingdoms of the Britons in "Hen Ogledd" ("the Old North"), the Brythonic-speaking parts of what is now southern Scotland and northern England.  The kingdom developed during the post-Roman period.  It is also known as Alt Clut, a Brittonic term for Dumbarton Castle, the medieval capital of the region.  It may have had its origins with the Brythonic Damnonii people of Ptolemy's "Geography".

Monte Arci: The Monte Arci is an isolated massif in the Uras plain in Campidano, Sardinia, Italy.  It is composed by three volcanic basalt towers, the highest one reaching an elevation of 812 m.  The inner part of the massif is composed of trachyte.

Rabbit Ears Pass: Rabbit Ears Pass (el.  9426 ft, 2873 m) is a high mountain pass in the Rocky Mountains of northern Colorado in the United States.  The summit has the shape of rabbit ears, which displays two large columns of basalt rock formations from the second volcanic episode.  Rabbit Ears Peak is underlain by a pink tuff and the basalt immediately to the west is underlain by red, vesicular ash.  Volcanic breccia occurs only at the Peak, which is a large stratified breccia pile.  The three basal layers are cut by a basalt dike immediately beneath the peak.  From petrographic evidence there appears to have been one period of lava flows and this surface can be seen at Rabbit Ears Peak.

Mare Anguis: Mare Anguis (the "serpent sea") is a lunar mare located on the near side of the Moon, about 150 kilometers in diameter.  Located within the Crisium basin, Mare Anguis is a part of the Nectarian System, meaning that it was formed during the Nectarian time period.  Like most mare, the surface of Mare Anguis is dark, indicating that it has been filled with volcanic basalt.

Diabase: Diabase ( ) or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro.  Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass).  "Diabase" is the preferred name in North America, yet "dolerite" is the preferred name in most of the rest of the world, where sometimes the name "diabase" is applied to altered dolerites and basalts.  Many petrologists prefer the name "microgabbro" to avoid this confusion.

Nürburg Castle: The Nürburg is a ruined hilltop castle in the German Eifel Mountains near the village of Nürburg south of Adenau in the district of Ahrweiler in the state of Rhineland-Palatinate.  It stands within the famous North Loop, or Nordschleife, of the Nürburgring racing course at a height of 678 metres on a volcanic basalt cone.  It may be visited for a fee.

Meridiani Planum: Meridiani Planum is a plain located 2 degrees south of Mars' equator (centered at ), in the westernmost portion of Terra Meridiani.  It hosts a rare occurrence of gray crystalline hematite.  On Earth, hematite is often formed in hot springs or in standing pools of water; therefore, many scientists believe that the hematite at Meridiani Planum may be indicative of ancient hot springs or that the environment contained liquid water.  The hematite is part of a layered sedimentary rock formation about 200 to 800 meters thick.  Other features of Meridiani Planum include volcanic basalt and impact craters.

Dumbarton Castle: Dumbarton Castle (Scottish Gaelic: "Dùn Breatainn" , ] ) has the longest recorded history of any stronghold in Scotland.  It overlooks the Scottish town of Dumbarton, and sits on a plug of volcanic basalt known as Dumbarton Rock which is 240 ft high.

Supporting paragraphs: Kingdom of Strathclyde Dumbarton Castle
Answer: 240 ft