But because the earth is tipped on its axis, as the moon orbits around the earth it moves higher and lower in the sky relative to the equator twice each month, thus shifting the position of the tidal bulges. Similarly, as the earth orbits around the sun, the sun moves higher and lower in the sky twice each year. Tides of maximum range, called tropic tides, occur twice a month when the moon is over the Tropic of Cancer or the Tropic of Capricorn. Tropic tides are particularly large in summer and winter when the sun is respectively highest and lowest in the sky. Tides of minimum range, or equatorial tides, occur twice each month when the moon is over the equator.
Tides are the largest single factor contributing to sea level changes in California.
Other influences such as storms, warming of the ocean water, and El Nino conditions raise the sea temporarily, and so far are not predictable. Intertidal plants and animals tend to occur in distinct bands, or zones, along the shore. Where organisms occur in the intertidal depends upon their varying responses to exposure to air, heat, and sunlight, predation or grazing, and competition for space. Some good places to observe intertidal life include Trinidad Sate Beach in Humboldt County, Shell Beach in Sonoma County, Fitzgerald Marine Reserve in San Mateo County, Point Pinos in Monterey County, Crystal Cove State Park in Orange County, and Children's Pool Beach in San Diego.