2000-P Sacagawea dollar struck on a Susan B. Anthony dollar T-2 clad planchet. An extremely rare transitional off-metal, which occurred when a leftover planchet used for striking 1999 SBA dollars was fed into a press striking 2000 Sacagawea dollars. The U.S mint was not striking SBA dollars in 2000, but only in 1999, and so probably at the end of the year some planchet were accidentally left in a press or in a coin bin, and then were struck by 2000 Sacagawea dies in 2000 when the mint would've started striking the new dollar coins. Because a Sacagawea dollar and an SBA dollar are the same diameter, this made it more likely and easier for an error like this to occur.
There are perhaps 6 or 7 known, making this an extremely rare transitional off-metal. Most have sold for $8000-$16,000 over the years, although they rarely come on the market except every few years, and are snapped up quickly. This coin grade PCGS MS-66, and has problem-free, lustrous surfaces. A beautiful coin.