Riyadh Region
Riyadh province:
 
Definition:
The name of Riyadh province is modern name not mentioned in the geography heritage books. At old times Riyadh province was included in what is called Al-Sa’eeda to indicate to all of Arabian Peninsula which we know nowadays. Riyadh province represents what is called Najd by the Muslim ****. It includes Najd with its two parts: upper Najd and lower Najd. It is located in the middle of kingdom of Saudi Arabia and considered the second biggest province after the eastern region in terms of area and the second after Mecca province in terms of population with a rate of 22.63% of the kingdom total population.
Riyadh province is characterized by being the starting point of country unification. It is center is in city of Riyadh, the country capital and the center of governance and management and the biggest urban center in the country. In spite of its natural qualities and its vast area, it is considered symmetric province in its qualities and characteristics from the geographic and historical perspective. Riyadh province is characterized with privacy among the kingdom of Saudi Arabia areas and this in the field of **** as it was the point from which thee*************. In addition, it includes the governance palace which represents the actual start of the kingdom kings from late king Faisal. The governance palace represents the ancient history and constructional heritage of Riyadh province in particular and the kingdom on general.
The privacy of this province occurred in two main axes of the country construction and establishment axes which are: the political axis and country structure and science and *** axis. In addition to the governance palace, the monuments and historical places in Riyadh city include Al-Musmak palacam Al-Muraba’ palace, Afif palace, Al-Shamisya palace, Al-Tarif district, and Manfouha tower.
With the issuance of the provinces system by royal decree number a/92 in 27/8/1412H which modified by royal decree number a/21 in 30/3/1414G which divides the kingdom of Saudi Arabia into thirteen provinces, Riyadh province became one of these provinces.
 
Location:
Riyadh province lies in the middle of kingdom of Saudi Arabia i.e. in the heart of it between longitudes 4200 and 4817 from east and latitudes 1900 and 2745 from north. It is bounded by the eastern region from the east, Najran province from the south, Aseer province from western south, and Mecca province and a part of Medina province from the west. Riyadh province extends towards the north to include Al-Artawya center which follow Al-Mujamma’a governorate at a distance of 305 kilometers and extends towards the south to Al-Khamaseen and the other centers of Wadi Al-Dawaser at a distance of 700 kilometers. It reaches in its northern and eastern boundaries to include the centers of Ramah governorate at a distance of more than 150 kilometers and its western extension reaches to Afif governorate and its centers at a distance of about 500 kilometers.
 
Area:
Riyadh province area is about (380.000) square kilometers or what is equivalent to about 17% of the kingdom area. With this area, it occupies the second position after the eastern region which area is one third of the area of kingdom of Saudi Arabia. Riyadh city which is the emirate headquarter and the capital of kingdom of Saudi Arabia lies in the middle of the eastern part of Riyadh province at 24° 39' latitude and 46° 43' longitude. This location provides Riyadh province with an important strategic dimension reflected positively on the development of Riyadh province in particular and the development of the surrounding regions in general.
 
Population:
Riyadh province comes after Mecca province in terms of population as its population is 5.188.286 people i.e. equal 22.63% of the kingdom population. The population density at Riyadh province is estimated with about (5.1) persons for each square kilometer. This rate is considered high if compared to the average population density in the kingdom which is estimated with about (4.6) persons for each square kilometer.
 
Climate:
At present time, Riyadh province has desert and continental climate characterized with heat and dryness in summer and coldness in winter with moderate but not ensured rate of rains. The daily and quarterly heat range is large. The rates of climate elements at Riyadh province differ from one governorate to another due to different atmospheric and geographic factors controlled by Allah divine power.
 
Terrains:
Riyadh province includes various terrains differ in west from east. In the west, there are igneous rocks characterized with their hard rocks and in the east there are sedimentary rocks with less hardness. The different factors of erosion resulted in the existence of different terrains and the waterways divided the main plateau into some plateaus. In upper Najd, there are huge valleys with long ways which its upper tributaries descend from Al-Hejaz mountains peaks.
 
The sedimentary plateau of Najd occupies most of Riyadh province area and composed of some rocky edges, plateaus, plains, and sand seas. The sedimentary rocks are well apparent in the Arab shelve in the middle of Arab peninsula in big bent strap along the eastern edge of the Arab shield constituting attractive symmetry edges in the inclination direction. The occurrence of edges phenomenon at the middle domain of kingdom of Saudi Arabia is due to the existence of sequence of sedimentary rocky layers different in their resistance to the water erosion processes. The edges are formed according to riverine erosion activity which at the end constitutes what is called the edge drainage systems. This system composed of four main types of rivers:
1- Original valleys or rivers: their flow direction corresponds with the rocky layers inclination direction and they penetrate all edges because they precede their formation like Al-Ramma valley, Al-Sahbaa valley, and Al-Dawaser valley. Geologically, they are called inclination valleys.
2- Subsequent valleys or rivers: their flow direction corresponds with the direction orthogonal to the rocky layers inclination direction like Hanifa valley.
3- Reverse valleys or rivers: they incline on the edges frontages, divide them, and create the evidences separated from edges frontages. They are responsible for their recession backwards. These valleys are characterized with severe inclination and they incline in direction opposite to the rocky layers inclination direction. They are called anti-inclination valleys.
4- Secondary valleys or rivers: They incline at the edge back and their inclination direction corresponds with the layers inclination direction. They are called secondary inclination valleys like Qudayya, Namar, and Laban valleys which incline on Tuwaiq and end in Hanifa valley which represents subsequent valley.
As an example of the valleys abundance in edges regions we mention the main valleys of Twuaiq edge which are: Nesah valley, Hanifa valley, Bark valley and its tributaries such as Raka valley and its tributaries Al-Sura valley and AL-Omk valley, Hawtet bani tamim valley, AL-Harik valley, Al-Aqeemy valley, Al-Sahbaa valley, Al-Dawaser valley and its tributaries.
There are also great valleys in which the floods of these valleys accumulate after crossing the edges region as Al-Sahbaa valley in which the floods of many valleys accumulate like Hanifa valley, Al-Sulai valley, Al-Aqwwmy valley, and Al-Sout valley through which Bark valley and its tributaries floods cross. Also, sands are prevalent in the western plateau (Upper Najd plateau) like Sabee branches, Nofod Al-Sura, Nofod Al-Awayned, Nofod Sabha, and Nofod Dhakan. This is inaddition to the sands prevalent on Najd lower plateau (edges region) like Nofod Al-Serr, Al-Deghebas branch, Al-Khobraa’ branch, Nofod Al-Thwairat, Areek Al-Bildan, and Nofod Al-Mulhaa’ in addition to the main sand seas such as Al-Dahnaa and Al-Rub’ Al-Khali.
It is worth mentioning that the highest point in Riyadh province is Sabha mountain (eastern south of Halban) whose height is 1524 meters above sea surface. Also, Qahtan pebble – lower pebble – is considered one of the highest regions in Riyadh province as its height is 1504 meters.
As for the lowest point in it, it is locates neat Kalmet AL-Hajara at the east of Dahnaa’ which its height is 297 meters. The highest point in Tuwaiq mountain is Farida Shana at Olaya region at the south of Hafira Nesah which its height is 1177 meters. The region lies at the east of Al-Hayania is considered one of the highest regions in Tuwaiq mountain as its height ranges between 1139 and 1141 meters.