1. Geographical location:

Yen Chau is a mountainous, border district of Son La province, located on National Highway 6, 240km northwest of Hanoi, 64km east of Son La city, a buffer zone between the two plateaus of Na San and Moc Chau, with geographical coordinates: 104°10’ - 104° 40’ east longitude, 21° 07’ - 21° 14’ north latitude, bordering Moc Chau district to the east, Mai Son district to the west, Bac Yen district to the north, and Lao PDR to the south, with over 56km of border. Map of Yen Chau district 2. 

2. Terrain: Yen Chau is a mountainous district, the terrain is fragmented and divided into two distinct regions: Yen Chau basin and border highlands. The basin area has 9/15 communes, located between the two plateaus of Moc Chau and Na San, at an average altitude of 400m above sea level. The border highlands have 6/15 communes, located at an altitude of 900 - 1000m above sea level, the communes are 30 - 70km from the district center.

3. Weather and climate:
The district belongs to the tropical climate zone divided into 2 distinct seasons: Rainy season from May to October, dry season from November to April of the following year, dry season often has prolonged cold, average annual temperature is 23°C, the highest temperature is 40.5°C, the lowest temperature is 17°C, the difference between day and night is quite high. Average humidity is 78.2%, lowest humidity is 38.7%.
4. About wind: Affected by north wind and northeast wind but not much, wind blows from October to February of the following year. The National Highway 6 area is affected by the dry and hot westerly wind (Lao wind), the wind usually blows from March to May.
5. Soil resources: Including many types of Ferlit soil developed on rocks, so it depends a lot on the properties of the parent rock, due to the origin of formation, it is divided into 3 main types: Mountain soil, humid tropical soil, and rice field soil.
6. Water resources: - The National Highway 6 area has 2 main stream systems: Sap stream system and Vat stream system. The Sap stream system originates from Moc Chau and other branches flow in such as: Huoi To Buong, Huoi Na Nga, Suoi Pha... and joins the Vat stream in Sap Vat commune. The water reserve is high but the usage value of this stream is still low, not well exploited, mainly serving daily life. The Vat stream system originates from the Khau Can range in Chieng Dong commune and other stream groups such as: Huoi Hit, Huoi Luu, Huoi Tum... entering the stream, the amount of water is not much but it is the main water source serving the production and daily life of the region. - The border highlands have the Nam Pan stream system flowing northwest to the Da river (Mai Son district), this stream only serves a small part of the communes of Chieng On, Yen Son, Phieng Khoai and focuses mainly on the Cho Long irrigation project.