Shaanxi is located in the middle of China, across the Yellow River and the Yangtze River. The area is long and narrow, with high terrain in the north and low terrain in the south. There are many kinds of landforms, including mountains, plains, plateaus, basins and canyons. From north to south, it can be divided into three regions: Loess Plateau in northern Shaanxi, Guanzhong Plain and Qinba Mountain in southern Shaanxi.
Loess Plateau in Northern Shaanxi The Loess Plateau in Northern Shaanxi is located in Fengxiang, Yaoxian and the north of Hancheng, which is the main part of the Loess Plateau in China. The terrain is high in the northwest and low in the southeast. 800 m to 1000 m above sea level. Except for some rocky mountains and beaches, most of them are covered with deep loess layers. The thickness of loess layer is mostly between 50 ~150m, and Luochuan is the thickest, reaching190m. The original edge was covered with large and small gullies, and some areas formed a landform with staggered floodplains and gullies.
Along the Great Wall, including Dingbian, Jingbian, Hengshan, Yulin and Shenmu counties in the north and Jiaxian county in the northwest, it is a beach zone, which is the southeast of the Mu Us Desert, and most of it is north of the Great Wall. From Dingbian to Kuye River, it is about 420 kilometers long from east to west and 12 to 120 kilometers wide from north to south. Dunes and sandy land are continuous. Mobile sand dunes are mainly distributed on both sides of Yuxi River, on the north bank of Wuding River, between Liuhong River and Luhe River, and in the area north of Dingbian. In winter and spring, the strong northwest wind makes the sand dunes move to the southeast continuously. The northern edge of the desert is an area where sand dunes, lake basins and beaches are staggered. Three sides (Dingbian, Anbian and Jingbian) Caotan basin has the widest beach. The middle of the beach is flat, with lush water plants in summer, which is suitable for agriculture and animal husbandry.
South of the aeolian landform area, there are mainly primitive, beam, headland, ditch and other loess landforms. Among them, the north of Yan 'an is the gully region and hilly region of Mao Liang, especially the Sui and Mi regions. Yan 'an, Yanchang and Yanchuan are the Liang Mao Gully areas dominated by beams. The west is the watershed of larger rivers, and there are many Liangshan mountains. South of Yan 'an is the former Lianggou area, which is dominated by the former. Luochuan is a well-preserved loess plain with a large area. Yichuan, Binxian and Changwu areas were eroded by valleys, forming a broken primitive. The valleys in the previous week were densely covered, generally as deep as 100 to 150 meters.
There are some short mountains with a relative height of several hundred meters on the plateau. Mainly: Bai Yushan, Ziwuling, Liangshan and Longshan. Beishan generally refers to a series of mountains in Guanzhong and northern Shaanxi Plateau north of Weihe River. A stony hill, partly covered with thin loess. It is still an inseparable part of the northern Shaanxi Plateau.
The larger rivers in northern Shaanxi flow into the Yellow River and the Weihe River respectively. The Yellow River Basin, the estuary where the Loess Plateau directly flows into the Yellow River and the river valleys passing through Beishan and Weibei Loess Plateau are all canyons. This valley is tens to more than 200 meters deep. The middle and upper reaches of major rivers and their main tributaries often form a wider land in Sichuan. Fertile soil, rich food.
Guanzhong basin is located between Qinling and northern Shaanxi Plateau, surrounded by mountains on three sides, narrow in the west and wide in the east. It starts from Baoji Gorge in the west and reaches Tongguan Port in the east, with a total length of about 360 kilometers. It was called "Qinchuan in 800 Li" in ancient times. The widest point east of Xianyang is more than 80 kilometers. The terrain is high in the west and low in the east, and the Weihe River flows eastward along the terrain. The basin is located on the fault block composite graben, with an altitude of 325 to 800 meters. It is composed of loess deposits and Weihe River alluvial deposits, with deep Cenozoic loose sediments. The Weihe River flows through, forming a vast terrace plain. The Weihe River is low and flat, with an altitude of 322 meters to 600 meters. The north and south sides are asymmetrical and stepped. It consists of floodplain, river terrace and loess plateau. Loess tableland is generally 200 to 500 meters higher than Weihe River. Terraces are distributed continuously on the north bank and incomplete on the south bank. The relative heights of terraces are different. Near Baoji, the first terrace is four or five meters higher than the normal water level of Weihe River, and the second terrace is ten or twenty meters higher. To the east of Xi 'an, the first terrace is five to fifteen meters high, and the second terrace is two to thirty meters high. The broad terrace plain is the main body of Qinchuan in 800 miles. Rich in water resources, flat terrain and fertile land. The eastern part of Guanzhong is located in the triangle of Yellow River, Weihe River and Luoyang River. The alluvial sand layer forms an east-west strip sand dune, which is the famous "sand garden" in Dali. It is 35 kilometers long from east to west and 6 to 10 kilometers wide from north to south.
The loess plateau is located between the second platform in Weibei and the northern Shaanxi Plateau. It gently inclines to Weihe River in a ladder shape, and the loess layer is more than 10 to 100 meters thick. The original surface is flat and distributed in continuous blocks. Due to the long-term perforation of Weihe tributaries, Weibei terraces are divided into Jia Cun Plain, Fufeng Plain, Xianyang Plain, Fuping Pucheng Plain, Chengcheng Heyang Plain and Hancheng Plain. The loess plateau on the south side of the Weihe River is narrow and continuously distributed, 250-400 meters higher than the Weihe River, and it slopes in a ladder or shield shape from the northern foot of the Qinling Mountains to the Weihe Plain. There are mainly Wuzhangyuan in Qishan, Nanshenhe Garden in Xi 'an, Shaocemetery, Bailuyuan and Yangguoyuan in Weinan, Chongning Garden, Gaotang Garden and Mengyin in in hua county. The original groundwater in the Loess Plateau is buried deeply, generally 40 to 70 meters, and the deepest part exceeds 100 meters. It is difficult to drink water and irrigate, so it is called "dry plain". The northern and southern edges of the basin, that is, the northern foot of Qinling Mountain and the southern foot of Beishan Mountain, are inclined plains of alluvial fans at the foothills. With less soil and more stones, rich diving, it is suitable for agriculture and forest.
Qinba Mountain area in the south of Guanzhong Basin in Shaanxi Province includes Qinling Mountain, Daba Mountain and Hanjiang River Basin sandwiched between them. The geographical structure of two mountains and one river is very obvious. When we mention Qinling Mountains, we can't help thinking of Where is the Hometown of Yunheng Qinling Mountains written by Han Yu, a great writer in the Tang Dynasty. Snow blocked the blue horse. Qinling Mountain is an east-west mountain range in China, which is the natural dividing line between geography, geology, climate and wildlife in China. Gansu and Qinghai in the west, Henan and Hubei in the east, and Shaanxi in the middle. One of the Qinling Mountains was first seen in Xi Du Fu of Han Dynasty. Qinling Mountain in Shaanxi lies between Weihe River and Hanjiang River Basin. It is 400 to 500 kilometers long from east to west and 120 to 180 kilometers wide from north to south. Altitude1500m to 3000m. It is steep in the north and gentle in the south, which is 1000 to 3000 kilometers higher than Guanzhong basin and Hanzhong basin. The main vein is distributed in the northern part of the mountain, and there are many peaks over 2000 meters, such as Huangyushan, Taibai Mountain, shouyangshan, Zhong Nanshan Mountain and Huashan Mountain, which constitute the high mountain and Zhongshan terrain of Qinling Mountains. The main peak is too white, with an altitude of 3767 meters. The Qinling Mountains west of Taibai are divided into three branches, namely Nanqi Mountain, Fengling Mountain and Baizi Mountain from north to south, all of which are above 2000 meters above sea level. From the south of Taibai Mountain to Yangxian County is the so-called "nine ridges and eighteen slopes", including nine ridges such as Qinggangling. To the east of Taibai Mountain, the Qinling Mountains are getting lower and lower, and the mountain structure in Shangluo area is divided eastward like a palm. The most famous people don't have such a thing as Mount Huashan in Xiyue, and they are known as "the five mountains are absolutely dangerous". Huashan Mountain, also known as Taihua Mountain, is located in the south of Huayang County and consists of five peaks and three valleys. Nanfeng, the main peak, is 2160.5m above sea level. This mountain is made of granite. Since Cenozoic, influenced by neotectonic activities, especially piedmont faults, Huashan Mountain has been rising continuously, forming a strange landscape with a relative height difference of 1700 meters from Guanzhong Basin. Due to the development of joints and fissures in granite, the mountains are high and steep, and numerous human landscapes form the unique Huashan culture in Sanqin culture. Qinling Mountain is a huge fault-block mountain, which was formed on the basis of folds, mainly composed of ancient metamorphic rocks and granite. The northern slope of Qinling Mountain is very steep, and the cliffs are towering, which shows the danger of Huashan Mountain. The canyon is deep, with many waterfalls, rapids and dangerous beaches. This deep canyon is customarily called "valley". Seventy-two valleys on the north slope have been traffic tunnels since ancient times. The famous Meridian Road, Oblique Road and Chencang Road all cross the Qinling Mountains along these canyons, and there are still many ancient plank road sites and ancient cliff calligraphy.
The mountainous area between Sichuan and Shaanxi is collectively called Bashan, with a length of about 300 kilometers and an altitude of 1.500 m to 2,000 m, which is higher than that of Hanjiang Valley 1.000 m.. It is a mountainous area dominated by limestone and granite. The folds and uplift faults are very strong, and the steepness in some places is no less than that in Qinling Mountains. Generally, it is lower and slower than the Qinling Mountains. Bashan is divided into two sections by Renhe River, with Micang Mountain in the west and Daba Mountain in the east. Affected by the east-west trend of the mountain and the different hardness of the rock strata, the rivers in Qinba Mountain area are divided north and south, and the beaches are dangerous and the water is urgent, forming a series of valleys alternating with canyons and dams. There are two river terraces in the dam, and farmland villages and towns are concentrated.
Hanjiang River runs through Qinba Mountain from east to west, forming a valley basin centered on Hanzhong and Anyuan. The Hanzhong Basin, from Wuhou Town in Mianxian County to Long Ting in Yangxian County, is about116km long, 5-25km wide and over 500m above sea level. It is a plain scoured by the Han River, with flat terrain and convenient irrigation, and is a "granary" in southern Shaanxi.
The western part of the Hanjiang River Basin belongs to the hilly area in the upper reaches of Jialing River, with gentle terrain and wide valley, which is the main land and water passage between Shaanxi and Sichuan.