If indeed, Moses wrote the Book of Genesis, some of the information contained therein is scientifically or historically invalid, so whatever his source it could not have been inspiration from God, in spite of 2 Timothy 3:16. It is then hard to imagine any other reliable source that would have told him that God made the whole world in six days, or that God made the earth and grew grass and plants before he created the sun as a light to rule the day (Genesis 1). Of course, he might have used sources such as the Babylonian creation story, if this was brought from Ur by Abraham and passed down to his day. On the other hand, so much of the biblical story of Abraham is contrary to history (such as meeting the Philistine king a thousand years before the arrival of the Philistines) that many historians believe Abraham never really existed.
Analysis of the Book of Genesis shows that it had more than one author, none of whom could have been Moses, whom tradition places in the second millennium BCE. However, knowing that the book was written later and by multiple anonymous authors (now known as the Yahwist, the Elohist and the Priestly Source) is not by itself enough to know the source of the information.
The first creation story (Genesis 1:1-2:4a) is attributed to the Priestly Source, writing during or shortly after the Babylonian Exile. It parallels a Babylonian creation account sufficiently to suggest that the author was influenced by the Babylonians.
There is a second, much older creation story in Genesis 2:4b-25. This is attributed to the Yahwist, who wrote quite early in the first millennium BCE. The Yahwist was strongly identified with the southern Hebrew kingdom of Judah and he must have recorded oral traditions extant in Judah at that time.
The biblical Flood story is remarkably similar to a similar story in the much earlier Epic of Gilgamesh, so either Gilgamesh was the source for Genesis or both accounts are based on an even earlier, common tradition. Ian Wilson, in Before the Flood reports credible evidence that the Flood was a folk memory of the inundation of the fertile plain that became the Dead Sea.
We do not yet have a consensus on the original sources of much of the information about the Patriarchs, but Genesis continued to be expanded right up to the sixth century BCE and later. Bruce Feiler says in Abraham, pages26-27, probably less than one per cent of the hundreds of stories about Abraham actually appear in the Bible.