The Yosemite National Park entrance is about an hour and a half from the Fresno area. If you're traveling to the area for the wedding and have an extra day to stick around, this could be a fun vacation opportunity! It is totally doable to do a day trip to Yosemite from Fresno if you get an early start. Keep in mind that between August 17th and October 27th, a reservation is required to enter the park between 5am and 4pm on Saturdays, Sundays, and holidays.
The Sequoia National Park entrance is also about an hour and a half drive from the Fresno area. If you can make an early start, it would be a great day trip for hiking among the giant sequoias!