The red stratum where Danxia Landform developed is called red bed by overseas scholars. Most red strata in China formed in the Mesozoic and Cenozoic, and those exposed in Sichuan are composed by lower Triassic, Jurassic and Cretaceous strata [24] . The Sichuan Basin had been in a sedimentary environment of large inland lake basin from the upper Triassic to the upper Cretaceous when red sediments were laid. The feldspar quartz sandstone is the chief component of the Danxia Landform in the South Sichuan (Figure 1). However, based on detailed field work, we found that those who are worthy of developing usually form in Cretaceous strata (each pentagram in Figure 1 represents a developed scenic spot or the one worthy of developing).

Regional structure is the main factor that gives rise to the Danxia Landform and affects its evolution. Large-scale regional structure controls the scale and distribution of Danxia Landform, while small-scale structure decides its appearance and form. When come to the regional structure controlling the formation of Danxia Landform, it usually refers to:

1) Bedding

Bedding is one of the primary structures. The red bed where Danxia Landform developed usually has horizontal or near-horizontal bedding stretching for tens of kilometres. Compared with horizontal or near-horizontal stratum, it is much easier to erode tilted stratum with higher angle, so Danxia Landform rarely developed in tilted strata. That is why strata where Danxia Landform developed in the South Sichuan commonly have horizontal bedding (Figure 2(a)) or lower angle which rarely exceeds 30 (Figure 2(b)).

2) Joints

Joints may occur in sets of parallel regularly spaced fractures and several sets may occur in the same rock, giving a conspicuous blocky appearance to an outcrop. Commonly, the formation of cliff and sharp-shaped Danxia Landform is related to vertical joints, while quadrate or house-like Danxia Landform is controlled by several joints sets which cutting each other. For example, house-like Danxia Landform at the Tianxiandong scenic area (Figure 2(c)) in Luzhou City is controlled by two joints cutting each other. The two joints cut the original huge rock to form fractures along the joint planes that are usually too feeble to stand prolonged weathering. Thousands or millions of years later, the soft components were erodes away or collapsed, while the hard part was left to form quadrate or house-like landform.

3) Faults

A fault is a planar fracture across which the rock has been displaced in a direction which is generally parallel to the fracture plane. Faults widely develop in the crust, thus it is one of the common structures in nature. Large-scale fault usually decides the framework of regional geology, and some are large enough to cut through the crust and gives rise to the basement rift. As Figure 1 shows, strata and Danxia Landform in the South Sichuan obviously controlled by large-scale faults, especially by the basement rift. Huayingshan Fault starts from Dazhou to the north and stretches to Rongchang and Yibin to the south [25] , with a length of approximate 600 km, controlling the deposit of Triassic and lower Jurassic strata and dividing the Cretaceous red bed in the South Sichuan into two parts. On the left side, Cretaceous strata are mainly distributed in the counties of Yibin, Muchuan, Jianwei and the central part of Leshan City, while on the right side, the Cretaceous strata concentrated in the counties of Jiang’an, Changning, Xuyong and Hejiang. The recent earthquakes occurred in Yibin is considered relevant to the movement of Huayingshan fault. Other faults, such as Emei-Yibin fault zone, Xinglongchang fault and Rongxian-Weiyuan fault are also controlling the formation of Danxia Landform in Yibin and Zigong.

During the formation process, like the joints, faults also play important role in controlling the appearance of Danxia Landform. As Figure 2(d) shows, serial deep vertical faults developed in Huagao Spring State Reserve Area, which cut the horizontal red strata into pieces and give rise to several sallow valleys. It is exactly where the Danxia Landform developed, indicating that the fault do control the appearance and distribution of the Danxia Landform.

Crust uplift after the formation of red bed constrains the development and evolution of Danxia Landform. The crust uplift carried deeply-buried rocks to the erosion basis. Due to the strong uplift, hills were cut by meandering rivers and formed steep slopes along both sides of the valleys gradually. Probably millions of years later, eminent Danxia Landform finally formed. In recent years, scholars prefer to adopt fission track to calculate the uplift pace, and the fission track age of minerals is considered the time when the mineral cooled due to the uplift of crust, because the mineral gets cooler when it is carried to the shallower depth as the uplift process. According to previous researches, since the late Cretaceous, the surface of Sichuan basin has suffered different erosion due to the collision and compression among plates, early slow uplift and cooling process (80 Ma - 20 Ma) and the late fast uplift erosion process(~20 Ma-today), respectively. The erosion speed of the different parts in the Sichuan basin significantly differs from each other. In space, the erosion speed gets faster from the northeast to the southwest. Since the late Cretaceous, Sichuan basin has been erased at least 2500 m, and in some parts over 4000 m [26] . It is exactly the intensive uplift that carried the late Cretaceous red strata to the erosion base level, getting the red strata exposed by weathering and running water, which formed the basic style and features of Danxia Landform.

For the formation of Danxia Landform in the South Sichuan, external forces mainly refer to weathering, running water and gravity.

Based on detailed field work, we found that the red strata in the South Sichuan are different in lithology. They consist of hard sandstones, glutenites bedded by mudstone, and soft siltstones. The hard stratum commonly is cemented by calcareous and ferruginous, with weak hydroscopicity but strong load intensity, thus it is hard to be eroded, while the soft stratum is mainly cemented by mud, with strong hydroscopicity but weak load intensity, which makes it easier to be eroded by weathering and rainfall [27] . Several outcrops in Tianxiandong in Luzhou indicate that how the weathering and rainfall erosion worked together to give rise to the formation of the caves in red strata. As Figure 3 shows, it is the soft stratum first started to crack because of endogenetic factors (Figure 3(a)), then the soft sediments was carried away by erosion and left many small holes (Figure 3(a)), and then the small holes grew bigger due to the continuous erosion and collapse (Figure 3(c)), and finally the bigger holes connected with each other along the soft stratum and formed large scaled bedding cave (Figure 3(d)).

The lateral erosion of running water also contributes to the formation of large scale horizontal caves at the foot of mountain, while the groundwater erosion is conducive to forming cliff and valley. Bedding caves caused by weathering and running water made the rocks above the cave hang in the air and the rock finally collapsed due to the gravity.

Besides religion-related scenery, Danxia Landform also contains abundant historic and cultural connotation, such as cliff tomb and cliff dwelling. Both the Mahao Cliff Tombs at the Leshan Giant Buddha scenic area and the Huangsanya Cliff Tombs at the Danshan Bishui scenic area in Yibin were built in the Han dynasty, indicating the ancient local residents’ living habits. In addition, cliff tombs at the Shichengshan are tombs built by the southwestern minorities from the Song dynasty to Ming dynasty, with remarkable significance in the appreciation and research of the culture of southwestern minorities.

In history, it was hard to conquer gate tower built on or between the mountains, because Danxia Landform is characterized by flat top and cliffy side. That is why there are so many ancient cities or villages ruins in the South Sichuan, such as Sangui Jiuding City at the Leshan Giant Buddha scenic area, Ziyun City at the Jianwei and Tianba village at the Bamboo Sea in the South Sichuan. What’s more, the calligraphy work caved on the cliffs, historical figures, minority customs, folk customs, diet habits and culture creations are valuable cultural resources awaiting developing. If the development of Danxia Landform can be integrated with the development of the aforementioned cultural resources, it will be conducive to enhancing the cultural soft power, improving the attractiveness of the scenic areas and disseminating and protecting local history and culture.

As natural scenery, Danxia Landform is of ample scientific connotation, referring to geography, geomorphology, geology, ecology, biology, environmentology and agronomy. New tourism products can be introduced by integrating the above scientific connotations with the nature sightseeing based on the analysis of tourists’ demands. That is exactly what is neglected by the decision makers nowadays.

How to excavate its geological connotation? It mainly refers to finding out the genesis of the red bed, formation time, forms of Danxia Landform, development mechanism, evolution, and the causes of the birth and death of palaeobios, the current situation and conservation of earth environment. The scientific connotation can be presented directly and vividly by using new information technology, such as VR and AR, which will not only provide the tourists with more smarter and comfortable experience but also foster awareness of seeking truth and protecting ecoenvironment.

To excavate the ecological connotation, we need to ravel out all plants and animals living in the scenic area, to tell tourists the species of special plants and their unique applications, to tell the tourists the name of different animals and their rarities, to inform tourists the environment destruction and enhance awareness of environment pretention. Scientific education and nature science experience can realize through plants exhibition, festivals, setting up plant varieties introduction and biology museum. In addition, we can explore the nearby agricultural resource and healthcare resources to operate leisure agriculture tourism, healthcare and hobby farm to prolong the sojourn time and further to improve economic returns.

To excavate the scientific connotation, we need to take the educational tourism into consideration. Educational tourism a tourism form supported by the state with large potential and is considered a new growth point. The development of Danxia Landform resource in the South Sichuan should be on based on the educational demand of tourists, which means various educational products should be developed according to different targeted customers. For example, for primary or middle school students, tour related to folk culture or local customs should be introduced, but for college students or adults, educational tourism related to professional subjects should be introduced. In recent years, the number of educational tourism consumers has kept growing with the implementation of relevant regulations on the educational tourism. The integration of Danxia Landform development and educational tourism will contribute to improving the scientific and cultural connotation at the scenic areas and keeping bring tourists in.