Asphalt deposits at Rancho La Brea, Carpinteria, McKittrick and Sulphur Mountain have been studied for insect remains. An astonishing number of species has been found varying in size from about 1 millimeter to 3 inches.
The four deposits studied present three distinct types: Rancho La Brea and Carpinteria were open pools due to upward surge of asphalt, with consequently constant movement in the liquid asphalt. The McKittrick field was due to chimneys opening on hillsides and the slow flow of the asphalt down the slopes caught many insects and small animals, with the larger animals only caught in the pools formed at the bottom. Sulphur Mountain is an almost vertical flow down a mountain side with small pools caught on ledges. Here as in McKittrick the insects are deposited where they die.
The stratification of the McKittrick field will permit climatic correlations and also studies in the gradual change of insect characters over a long period of time.
The finding of certain carrion insects indicates the time required for complete submersion of the animal. This took up to three months at La Brea, but two to three years at McKittrick.
The large number of aquatic insects in the deposits poses a number of interesting questions.
The continuous deposition of asphalt from Middle Pleistocene to this day gives a wonderful opportunity for paleoecological study.