Here are a couple of photos of the Chiba Clock Tower at the north end of McCarthy Park on Swan Island. A sign at the base has a short inscription:
This solar clock tower was presented to the people and Port of Portland by Mr. Takeshi Numata, Governor of Chiba Prefecture and the administrator of the Port of Chiba, on June 5 1987. The Port of Portland and the Port of Chiba became sister ports in November 1980 to enhance the friendship and prosperity of the United States and Japan.
Apparently a "sister port" is like a sister city relationship between local port authorities, and Portland has several of these, also including Ulsan, South Korea (which also a sister city of ours) and Tianjin, China. This is in addition to Portland's half a dozen or so "regular" sister cities.
Apart from what the sign tells us, I don't know a lot about this clock. I found a city document comparing Port of Portland recreation facilities w/ other West Coast cities, which mentions the clock in passing, but that's about it. The library's Oregonian newspaper database doesn't seem to have anything about the clock, specifically, but it does tell us the gift-giving was mutal, as Portland shipped a Lelooska totem pole to Japan in 1986. (Lelooska also created the large totem pole next to the Chart House on Terwilliger, and various others around the area.)
You'd think a solar-powered clock from Japan would be a beloved local landmark in 2015 Portland. You'd think hipsters would ride their fixie art bikes to the solar clock and picnic on artisanal donuts and PBR while strumming their ukuleles, and then the tourist guidebooks would find out about it, and senior tour groups from Kansas would show up in giant buses to view Portland hipsters in their native habitat or something. But due to the weird out-of-the-way location, none of this seems to have happened, at least not yet. But at least this way I can talk about the Chiba Clock Tower and say "you probably haven't heard of it", for whatever that's worth.