Apart from the Boulder Tombs of the Anning River watershed in Liangshan, experts have also studied other finds in the prefecture bronze weapons at Yanyuan County, as well as stone coffins and residential ruins in Huili County.

In recent years, farmers in Yanyuan have often stumbled upon cultural relics as they worked in the fields. Archaeologists have also found various swords, arrows, knives and armours in the county.

According to Liu Hong, curator of the Liangshan Prefecture Museum, cultural relics from Yanyuan County are quite special in Southwest China. The bronze ware here can be compared with that of Sanxingdui and Jinsha, two important prehistoric ruins in Sichuan.

Over 70 per cent of the cultural relics found at Yanyuan are weapons, indicating that a strong people lived along the Yalong River from the Warring States Period (475-221 BC) to the Western Han Dynasty (206BC-AD 24).

Liu said they might have been the Ze people, ancestor of today's Naxi ethnic minority.

In 1991, experts found the remains of a warrior from Laolongtou in Maojiaba. The warrior, who was 190 centimeters tall, was buried with a 30-centimeter iron spear and many other weapons.

In Chinese, Yanyuan means "source of salt." In ancient China, salt was a precious resource. People who had control of salt had to have strong defences, or they would be attacked and driven away by other tribes, Liu said.

At Nange Township in Huili County, researchers discovered a 3,500-year-old residential area called the Dongzui Ruins.

As the area containing the Dongzui Ruins was threatened with soil erosion from the Malong River, archaeologists excavated 70 square meters. During this work last December, they found the base of six rooms. The largest and most intact room was 4.6 meters by 3.8 meters.

Besides pottery and stoneware, a jar was found in another room. These objects look different from those found in the Anning River, representing a different ethnic minority culture, Liu said.

A preliminary survey indicates more than 10,000 square meters of similar houses are in the surrounding area of the confluence of the Chenghe and Malong rivers.

"River confluences are the best places for human settlement," Liu said. "Since we found few hunting tools, we presume that the inhabitants here relied on agriculture."

Before the residential area was found, experts already discovered over 100 stone coffin tombs in a dozen groups along the Chenghe River at Huili. All the rectangular tombs were built with stone slabs.

Tang Xiang from the Huili Cultural Relics Institute said five items of pottery and one piece of stoneware were found with 17 human remains during an excavation of 20 such tombs at Xiaoyingpan in 2002.

What was special about the human remains was that none of them were intact: Some skulls were cut and they were placed at the chest or abdomen while others were missing fingers or toes.

The stone coffins could date from between the late Neolithic period to Western Han Dynasty, said Tang. Similar tombs were found in Caiyuanzi in Yongren County, Yunnan Province. Both are the oldest stone coffins found so far in Southwest China.

A special burial custom involving the severing of limbs was once popular among some ancient tribes in Southwest China, and thus the excavation could lead archaeologists to figure out who built the tombs.

According to historical records, some Di and Qiang tribes moved along the Hengduan Mountains and settled at Huili. They intermingled with the local people and created a unique culture.

Stone coffins seemed to disappear after the Western Han Dynasty, whose rulers strengthened their control over the minority regions.

"In the Han Dynasty, Huili was called Huiwu. That was the first written record about the county," said Liu Hong. "The excavations are important for understanding the history of Huili and the whole of Liangshan."