St. Stupid's Day (April 1)

Migration of Grey Whales (seasonal North & South)

http://www.oceanicsociety.org/graywhales

Cherry Blossom Festival (in Japantown)

http://www.nccbf.org/

Commemoration of 1906 Earthquake - April 18, 5:12am at Lotta's Fountain, Market St. x Kearny St.

San Francisco International Film Festival

http://www.sffs.org/

Spring Native Plant Garden Tour

http://www.cnps-yerbabuena.org/gardens/annual_garden_tour.html

Strybing Arboretum Plant Sale

The San Francisco Natural History Series

http://sfnhs.wordpress.com/

  Critical Mass Bike Ride

(begins at east end of Market St on the last Friday of the month at about 6pm)

http://critical-mass.info/