Take a look at the document on the right. The man's name is an attention-getter, but it's really a distraction.
The important question is why did it require a private act of Congress to permit George W. (for Washington, not Walker) Bush to own the land he had been farming for ten years? Everyone agreed that he was one of the most important pioneers in the northwest, so why couldn't he claim and own a piece of land like every other settler did?
The answer: because he was a Mulatto, and African-Americans were not permitted to own land in Washington Territory.
This gentleman was arguably more interesting than the various other George Bushes that have come along since. A successful merchant, Bush subsidized other members of the wagon train that he and his family used to cross the Oregon Trail. Some of the settlers chose to defy the Hudson Bay Company and become the first Americans to settle north of the Columbia River, because Bush could not live in Oregon (to keep slavery out, they had banned all Blacks). When the first winter hit Bush was one of the very few farmers with crops in the ground and he shared them with his neighbors when he could have made a profit instead.
I remember reading a discussion of Bush's birth year and one historian said, approximately, that of the several possible he was choosing the least likely because, in the case of this man, the least likely usually turned out to be correct.
Why hasn't Hollywood made a movie about this guy?
You can see the full text of the committee report (2 pages) here and here.