An alkali sink is a salty basin land form. In these depressions, which are found only in the San Joaquin Valley, California, rainwater drains to the basin and collects in areas where it cannot penetrate the soil due to a hard layer of clay or caliche, producing a pond or lake. When the water evaporates, it leaves behind increasing amounts of salt and minerals in the soil, creating a high pH level in the water and soil.