Silverwood Theme Park is certainly the largest of its kind in the inland Northwest. Started in 1988 with an old West mining town theme, the park now covers nearly 200 acres with almost 60 rides and attractions. piercing the skies at Silverwood is a rooler coaster called Aftershock, Tremors, is a 65-mph wooden coaster that drops about 100 feet and shoots underground around and also has a water park there as well.