The volcano was built up above the surrounding country by repeated eruptions and successive flows of lava. It is a relatively young volcano, only about 500,000 years old. By contrast the mountains of the Cascade Range that Mount Rainier looks down upon are at least 12 million years old! 3. What is the annual visitation to Mount Rainier? 3. How many people climb the mountain each year? In 2018, 10,762 people attempted to climb Mount Rainier; 5,135 of them actually reached the summit. 4. Is the park open all year? 4. Is Mount Rainier an active volcano?