Nobody knows for sure how far back the Naxi pictographs date. But we can glean some clues from the pictographs themselves. Interestingly, the pictographs for North, 
ho33 gɣ33 lo21, and South, 
i33 tʂʼɪ33 mɯ21, when combined, form the character for water, 
dʑi21. Li Jingsheng 李静生 speculates that the reason for this is that the Naxi were living in an area where a river flowed from north to south at the time of the creation of the north/south pictographs. We know that the Naxi are descendants of the ancient Qiang tribes of Northwest China, who migrated south and finally settled in Lijiang. During this migration, the only time that they were settled in an area with a river flowing north-south was during the late Shang (1600-1046 BC) and early Zhou (1045 BC-256 AD) dynasties, when the Naxi settled by the upper reaches of the Min River 岷江 in Sichuan, a tributary of the upper Yangtze. If the pictographs originated during this period, then that would make them of similar age to the oracle bones (most of which date to the last few centuries of the Shang dynasty).
Li adds to this theory by looking at the pictographs for the four seasons, which depict the climatic conditions associated with the particular season. The pictograph for Spring,
ŋy21, clearly indicates that this is the windy season (the character is composed of sky + wind). Likewise, the character for Summer, 
ʐu21, shows the rainy season (sky + rain). Autumn, 
tʂʼɣ55, depicts a flower in bloom (sky + flower) and Winter , 
tsʼɪ33, is of course snow (sky + snow). The problem here is with Autumn . Flowers do not bloom in the Autumn months in the Lijiang basin, so why should the pictograph depict the flower? Li suggests that the pictograph originates from a time when the Naxi people were settled in an area with autumn flowering plants. The History of the Qiang People 《羌族史》 notes:
ho33 gɣ33 lo21, and South, i33 tʂʼɪ33 mɯ21, when combined, form the character for water, dʑi21. Li Jingsheng 李静生 speculates that the reason for this is that the Naxi were living in an area where a river flowed from north to south at the time of the creation of the north/south pictographs. We know that the Naxi are descendants of the ancient Qiang tribes of Northwest China, who migrated south and finally settled in Lijiang. During this migration, the only time that they were settled in an area with a river flowing north-south was during the late Shang (1600-1046 BC) and early Zhou (1045 BC-256 AD) dynasties, when the Naxi settled by the upper reaches of the Min River 岷江 in Sichuan, a tributary of the upper Yangtze. If the pictographs originated during this period, then that would make them of similar age to the oracle bones (most of which date to the last few centuries of the Shang dynasty).Li adds to this theory by looking at the pictographs for the four seasons, which depict the climatic conditions associated with the particular season. The pictograph for Spring,
ŋy21, clearly indicates that this is the windy season (the character is composed of sky + wind). Likewise, the character for Summer, ʐu21, shows the rainy season (sky + rain). Autumn, tʂʼɣ55, depicts a flower in bloom (sky + flower) and Winter , tsʼɪ33, is of course snow (sky + snow). The problem here is with Autumn . Flowers do not bloom in the Autumn months in the Lijiang basin, so why should the pictograph depict the flower? Li suggests that the pictograph originates from a time when the Naxi people were settled in an area with autumn flowering plants. The History of the Qiang People 《羌族史》 notes:
“羌族分布在青藏高原东部边缘,山脉重重，地势陡峭，地面有岷江，黑水河。。。初秋时节，河谷正是紫罗兰盛开，而高山却是白雪皑皑”
“The Qiang were spread across the Eastern edge of the Tibetan plateau, a steep mountainous area through which the Min and Heishui Rivers flow…in early autumn, violas bloom across the river valley, and yet the mountaintops reveal an expanse of white snow.”
This shows the reasoning behind the flower in bloom as a symbol for autumn. From this Li backs up his claim that the Naxi were living by the Min River at the time of the character’s creation, dating the pictographs to the Shang/Zhou dynasties.
