High Quality Content by WIKIPEDIA articles! Mount Si High School is a high school located in the Snoqualmie Valley in Snoqualmie, Washington and a part of Snoqualmie Valley School District #410.GreatSchools.net rates MSHS at an 9 out of 10 with a community rating of 3 out of 5. GreatSchools.net lists MSHS`s highlights as its academic contests, bands, and basketball. The school also served as the basis for Twin Peaks High School, in the cult classic drama, Twin Peaks.