Hey there HMBF,
Bummer about the summit register. I don't understand that kind of ****, and don't try to.
The summit register is maintained by the Mazamas (see Mazamas.org) in cooperation with the Oregon Dept of Forestry, who manage the Tillamook State Forest. The log books from this and other summits are kept in the Mazamas archives (office is located on NW 19th Street, in Portland. A great and really extensive mountaineering & travel library is open to the public).
I'll let the office know tomorrow about the vandalism.
Sorry it bummed your day. But hey, you still climbed 2800' to the top of a beautiful hill - good going!
After winter, try the full Elk Mtn - King Mtn traverse loop for a good workout, you'll have earned your ale