The city Parks & Rec Bureau's page on Washington Park says:
A bronze statue of Sacajawea holding her son Jean-Baptiste is located near the Chiming Fountain. In commemoration of the heroic Shoshone Indian woman who helped lead the Lewis and Clark explorers through the mountains of the west, the statue was unveiled on July 7, 1905 at the Lewis and Clark Centennial. Among those present at the event were Susan B. Anthony, Abigail Scott Duniway, and Eva Emery Dye. The project was promoted and paid for by subscriptions solicited nationwide by a group of Portland women headed by Mrs. Sarah Evans. The committee commissioned Alice Cooper of Denver, at that time an understudy of Lorado Taft, to sculpt the statue. It was cast in New York and required 14 tons of copper which came from the Sweden mine, just below Mt St Helens. The copper was donated by Dr. Henry Waldo Coe of Portland. In April 1906, the statue was placed in its current location in Washington Park. Its inscription reads, "Erected by the women of the United States in memory of the only woman in the Lewis & Clark expedition, and in honor of the pioneer mother of Oregon."
A post at Portland Public Art has a bit more background about the piece. It's not a snarky post, which is unusual; the post you're reading now isn't meant to be snarky either; I generally roll my eyes at vintage statues of Indians made by white people. This one's sort of different in that it depicts (or at least symbolizes) a beloved historical figure. Note the fresh flowers at the base and what appears to be lipstick on the statue.
Normally this would be the point where I explain that a certain beloved historical figure was overrated or misunderstood or something. I even started trying to write that tangent a few times, but they were just wordy ways of saying "Nobody Knows". I can't even get snarky about people filling in the gaps with mythology or wishful thinking, since that's pretty much what happens with all historical figures to some degree. So I think I'll just leave it at that.