Simpson Investment Company
The Simpson Investment Company is a company based in the US Pacific Northwest that specializes in manufacture of forest products. Founded as a logging company in 1890 by Sol Simpson, the company now functions as a holding company for the Simpson Door Company, a manufacturer of wood doors.
Simpson announced in 2008 that it will be entering the "green power" industry by building a new power plant at its Tacoma Tideflats mill that will generate power via the burning of sawmill and other forest waste. In August 2009, construction of the power plant was completed. It generates 55 megawatts of power which is sold to Iberdrola Renovables and used by the Sacramento Municipal Utility District. 
The company was split into two units in 2006. The Green Diamond Resource Company is a spinoff that was created to manage Simpson's forest lands. Both companies are owned by the same shareholders and as with the current subsidiaries, function as separate departments within a large company rather than as completely independent companies.
The Simpson Lumber Company conducted logging operations and was based in Shelton, Washington. Four mills were sold to Interfor and the Shelton property was sold to Sierra Pacific Industries.  The Simpson Tacoma Kraft Company produced pulpwood and linerboard products. The "Simpson Tacoma Kraft Company", was sold to RockTenn in 2014.
The Simpson Company built and operates a logging railroad known as the Simpson Railroad. It is one of the last logging railroad operations in the continental United States and dates back 120 years. The railroad was once extensive and branched out into several hundred miles of forestland in the Olympic Peninsula but is now limited to ten miles of operational track. The rail line was to transport lumber and as a transportation network to remote logging camps and towns. Construction of the railroad line was an engineering feat as demonstrated by the large and complex bridges built to span gorges and the mountainous terrain the railroad traveled through. The Vance Creek Bridge and the High Steel Bridge were built in 1929 and used until the 1980s when the line was abandoned. The Vance Creek Bridge still stands, and the High Steel Bridge is still in use as a forest road. The High Steel Bridge is one of the tallest rail bridges in the United States and has been listed in the National Register of Historic Places.
- John Gillie (2008-04-28). "Simpson Investment Co. will build power plant at Tacoma Tideflats mill". Tacoma News Tribune. Retrieved 2009-08-31.
- "New Tacoma biomass plant starts churning power". Puget Sound Business Journal. 2009-08-11. Retrieved 2009-09-06.
- Chris Genna (2006-06-25). "Simpson splits units but keeps focus". Puget Sound Business Journal. Retrieved 2009-08-31.
- Interfor purchases four U.S. sawmills
- Simpson Selling Remaining Lumber Assets to SPI
- Georgia company agrees to buy Simpson Tacoma Kraft paper mill
- "Heavy Lifting". Shelton-Mason County Journal. 2007-03-22. Retrieved 2009-09-01.[dead link]
- National Park Service (2007-01-23). "National Register Information System". National Register of Historic Places. National Park Service.
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