Fúsāng (扶桑), the Leaning Mulberry

The Classic of Mountains and Seas (Shānhǎi Jīng 山海經) is a compilation of mythological texts from well before the Hàn dynasty, i.e., from a period of time when the Chinese had a completely different set of religious sytems than in Imperial times — see p35-36 of The Celestial Empire.

As per the shamanic part of the archaic belief system, the sun was believed to rise from a gigantic mulberry tree in the far east, called the Leaning Mulberry (fúsāng 扶桑). This tree is obviously an axis mundi type of tree, common to all shamanic belief systems. The interesting difference here is that the fúsāng is supposed to be in the far eastern end of the world rather than at its centre.

The sun would follow the leaning branch of the mulberry tree above the earth, up to the far western end of the world: the Kūnlún Mountains. There, depending on the version of the myth, the sun would either die and be reborn the next day in the east, or it would be carried back by a three-legged crow (sānzúwū 三足烏) or in a carriage driven by the sun goddess (Xīhé 羲和). In any case, these myths were already considered as being non-historical in the late Hàn.

It is interesting to note that the earliest versions of the myth mention ten suns, who would travel round the sky one after the other. This could be the origin of the ten heavenly stems.
One day, the ten suns all set out at once by mistake, threatening the burn the world. Hòuyì (后羿) the archer saved the day by shooting down all but one of the suns. Hòuyì is celebrated at the Mid-Autumn Festival, see p14 of TCE.