San Diego in hardiness zone 11, with the last freeze having occurred many decades ago. Annual rainfall along the coast averages and the median is . The months of December through March supply most of the rain, with February the only month averaging or more. The months of May through September tend to be almost completely dry. Although there are few wet days per month during the rainy period, rainfall can be heavy when it does fall. Rainfall is usually greater in the higher elevations of San Diego; some of the higher areas can receive per year. Variability from year to year can be dramatic: in the wettest years of 1883/1884 and 1940/1941, more than fell, whilst in the driest years there was as little as . The wettest month on record is December 1921 with . Snow in the city is so rare that it has been observed only six times in the century-and-a-half that records have been kept. In 1949 and 1967, snow stayed on the ground for a few hours in higher locations like Point Loma and La Jolla. The other three occasions, in 1882, 1946, and 1987, involved flurries but no accumulation. On February 21, 2019, snow fell and accumulated in residential areas of the city, but none fell in the downtown area. Ecology Like much of Southern California, the majority of San Diego's current area was originally occupied on the west by coastal sage scrub and on the east by chaparral, plant communities made up mostly of drought-resistant shrubs. The steep and varied topography and proximity to the ocean create a number of different habitats within the city limits, including tidal marsh and canyons. The chaparral and coastal sage scrub habitats in low elevations along the coast are prone to wildfire, and the rates of fire increased in the 20th century, due primarily to fires starting near the borders of urban and wild areas. San Diego's broad city limits encompass a number of large nature preserves, including Torrey Pines State Reserve, Los Peñasquitos Canyon Preserve, and Mission Trails Regional Park. Torrey Pines State Reserve and a coastal strip continuing to the north constitute one of only two locations where the rare species of Torrey Pine, Pinus torreyana, is found. Due to the steep topography that prevents or discourages building, along with some efforts for preservation, there are also a large number of canyons within the