Goldendale Observatory State Park, State park observatory in Goldendale, Washington, US.

Goldendale Observatory State Park is a five-acre public observatory on a 2,100-foot hill north of Goldendale, Washington. Its South Dome, 20 feet across, houses a 24.5-inch Cassegrain reflector built by four amateur astronomers; a 10-foot North Dome and a Hydrogen-Alpha solar telescope stand nearby. The site also has an interpretive center, amphitheater and picnic area, reached by a winding paved road through an oak forest.

Four amateur astronomers built the 24.5-inch Cassegrain reflector for Clark College in Vancouver, Washington, which paid for the materials; the college then sought a darker site and donated it to Goldendale on condition the town build an observatory. The Goldendale Observatory Corporation was founded in 1971, the cornerstone was laid in May 1973, and the facility was dedicated on October 13, 1973. Washington State took over the site and its debt in 1980, and the park became a state park heritage site in 2014.

The observatory was conceived from the start as a center of public science education, not research. Its 24.5-inch telescope was built by four amateurs and donated on condition the town build a dome for it. Weekend public viewing is by appointment, and the site also hosts an annual astronomy event.

Visitors need to schedule visits in advance, as the facility operates on a limited schedule throughout the year. Operations run Thursday through Sunday from April to September, then shift to Friday through Sunday from October to March.

The 1979 eclipse made the observatory the Astronomical League's headquarters, and NBC set up cameras at the telescope for a live broadcast. Around 15,000 people came to Goldendale that 26 February; the German source gives 17,000. The attention ended the financial troubles that had raised closure plans in 1978.