From deserts, crowded cities, and rugged coastlines to the farmlands of the Central Valley, California encompasses some of the most diverse natural habitats on the planet. California is part of a global biodiversity hotspot (the California Floristic Province) with plants and animals in abundance, many found nowhere else on Earth. Unfortunately, the state’s spectacular biodiversity is seriously threatened: at least 75% of the original habitat has already been lost. It is imperative to develop a new baseline of California biodiversity and to monitor how exactly change is accelerating. However, scientists alone cannot thoroughly monitor biodiversity. We need everyone to share the nature they find everywhere - in your backyard, in your schoolyard, in your favorite parks, and growing in the cracks in the sidewalk - to help build a comprehensive picture of biodiversity in California. What better way to help create a baseline of California biodiversity than to capitalize on the friendly rivalry between San Francisco and Los Angeles and engage in a biodiversity competition? Centered around National Citizen Science Day and Earth Day, the California Academy of Sciences and the Natural History Museum of Los Angeles County are asking residents of and visitors to the San Francisco Bay Area and Los Angeles County to explore nature all around them and document the species they find using iNaturalist. At the end of the week, we’ll compare stats like total number of species found, total number of observations, and total number of observers to find out who comes out on top: Los Angeles or San Francisco!