Question: What long, steep, narrow mountain range provides a controversial border that splits Maryland into two parts?

Context paragraphs:
Sangre de Cristo Range: The Sangre de Cristo Range, called the East Range locally in the San Luis Valley, is a high, rugged and narrow mountain range of the Rocky Mountains in southern Colorado in the United States, running north and south along the east side of the Rio Grande Rift.  The mountains extend southeast from Poncha Pass for about 75 miles (120 km) through south-central Colorado to La Veta Pass, approximately 20 miles (32 km) west of Walsenburg, and form a high ridge separating the San Luis Valley on the west from the watershed of the Arkansas River on the east.  The Sangre de Cristo Range rises over 7,000 feet above the valleys and plains to the west and northeast.

Elbe Sandstone Mountains: The Elbe Sandstone Mountains, also called the Elbe sandstone highlands (German: "Elbsandsteingebirge" ; Czech: "Labské pískovce" ) is a mountain range straddling the border between the state of Saxony in southeastern Germany and the North Bohemian region of the Czech Republic, with about three-quarters of the area lying on the German side.  The mountains are also referred to as Saxon Switzerland and Bohemian Switzerland in both German and Czech ("Sächsische Schweiz" and "Böhmische Schweiz" in German, "Saské Švýcarsko" and "České Švýcarsko" in Czech) or simply combined as Saxon-Bohemian Switzerland.  In both countries, the mountain range has been declared a national park.  The name derives from the sandstone which was carved by erosion.  The river Elbe breaks through the mountain range in a steep and narrow valley.

Sideling Hill: Sideling Hill (also Side Long Hill) is a long, steep, narrow mountain ridge in the Ridge-and-Valley (or Allegheny Mountains) physiographic province of the Appalachian Mountains, located in Washington County in western Maryland and adjacent West Virginia and Pennsylvania, USA.  The highest point on the ridge is Fisher Point, at 2310 ft in Fulton County, Pennsylvania.

Qaflankuh Mountain Range: Qaflankuh or Qaflankuh Mountain Range (Persian: رشته کوه‌ها‌ی قافلانکوه / Reshteh Kuh-hā-ye Qāflānkuh) is a mountain range that is located about 20 kilometres north of the city of Zanjan in Zanjan Province, Iran.  With an average width of almost 20 kilometres and a length of about 100 kilometres, this mountain range is stretched in a northwest-southeast direction, beginning from northwest of Zanjan, passing north of Zanjan and ending southeast of Zanjan.  The Qezel Owzan River flows in a valley that separates Qaflankuh Mountains on the south from Talish Mountains on the north.  With an elevation of 2971 metres, Mount Sendan Dagh is the highest mountain of the range which is located in the southeast section of this mountain range.  There are some mineral hot springs containing sulphur in different parts of this range.  Geologically, Qaflankuh Mountain Range was formed during the Tertiary volcanism and plutonism and is made mainly of the Eocene volcanic rocks with very small sections of intrusive rocks in the northern and southern parts of the range.

Krucze Mountains: The Krucze Mountains (Czech: "Vraní hory" , German: "Rabengebirge" Polish: "Góry Krucze" ) are the Eastern part of the Stone Mountains, which belong to the Central Sudetes on the border of the Czech Republic and Poland.  To the West and North-Western part the mountain range borders the Lubawska Plateau and the Karkonosze Mountains, to the North-Eastern part they border the mountain range Czarny Las, from the East they border the sediment basin Kotlina Krzeszowska and the Zawory mountain range and to the South the mountain range borders the Czech part of the Stołowe Mountains.  To the Southern ridge of mountain range is the Polish-Czech border.  The border crossing for cars is in Lubawka and for tourists is in Okrzeszyn.

Montara Mountain: Montara Mountain, positioned between the unincorporated community of Montara, California to the southwest and the city of Pacifica, California to the north, forms the northern spur of the Santa Cruz Mountains, a narrow mountain range running the length of the San Francisco Peninsula that separates San Francisco Bay from the Pacific Ocean.  Its highest point rises to 1898 ft above sea level.  An unpaved fire road, the North Peak Access Road, accessible from the Pedro Mountain Road in McNee Ranch State Park, provides access to the summit by hikers from the south.  From the north, Montara Mountain Trail, Hazelnut Trail and Brooks Creek Trail provide access to the mountain with trailheads in San Pedro Valley County Park.

Western Maryland: Western Maryland is the portion of the U.S. state of Maryland that traditionally consists of Washington, Allegany, and Garrett counties, with western portions of Frederick County also associated with the area.  The region is bounded by the Mason-Dixon line to the north, Preston County, West Virginia to the west, and the Potomac River to the south.  There is dispute over the eastern boundary of Western Maryland.  For most residents of the Baltimore-Washington area, everything west of Frederick city is considered Western Maryland.  However, the people of the more mountainous and isolated Allegany County and Garrett County consider Sideling Hill the boundary between Western Maryland and what they refer to as "down-state."

Boomerang Range: The Boomerang Range, (at ), is a narrow mountain range on the western side of the Skelton Glacier and Skelton Névé, Antarctica.  The range is curved like a boomerang, and extends generally north-south for about 25 km.  It was mapped and named in 1957 by geologists in the New Zealand party of the Commonwealth Trans-Antarctic Expedition (CTAE), 1956-58.

Lazikou Pass: The Lazikou Pass () is a narrow mountain pass in the Min Mountain Range, Têwo County, Gannan Tibetan Autonomous Prefecture, southern Gansu, China.  The pass forms a gateway between northwestern Sichuan and southern Gansu.  It is of historical significance due to its strategic importance in the final phase of the Long March.

Yandang Mountains: Yandang Mountains or Yandangshan (Chinese:  雁蕩山 ,  雁荡山 ,  "Yàndàng Shān",  "Wild Goose Pond Mountain(s)") refers, in the broad sense, to a coastal mountain range in southeastern Zhejiang province in eastern China, covering much of the prefecture-level city of Wenzhou (from Pingyang County in the south to Yueqing County in the northeast) and extending to the county-level city of Wenling in Taizhou prefecture.  The mountain range is divided in two by the Oujiang River, the two parts being the North Yandang and South Yandang.  More narrowly, Yandangshan is also used more narrowly to refer to Mount Yandang , a specific part of the North Yandang around an ancient caldera near a small town of the same name (雁荡镇 , "Yàndàng Zhèn").  The highest peaks of North Yandang are located here, and this is also the main tourist spot.  In this article, name "Yandang Mountains" is used to refer the mountain range and "Mt. Yandang" to refer to the caldera.

Supporting paragraphs: Western Maryland Sideling Hill
Answer: Sideling Hill