LOS ANGELES — No one expects to stumble across a cache of Picasso’s works in the middle of a desert. So who would think that just off bustling Wilshire Boulevard, tucked between the Los Angeles County Museum of Art and the national headquarters of the Screen Actors Guild, lie buried some of the most exquisitely preserved fossils in the world?

The fossils of the La Brea Tar Pits are just that. They were first discovered in Maj. Henry Hancock’s asphalt mine in the 1870s, when Los Angeles was but a village. Since the early 20th century, more than one million bones have been excavated from the pits; when reassembled, they provide an extraordinary time capsule of the creatures that roamed Southern California 10,000 to 40,000 years ago.

Interest in these animals today, however, is more than a matter of prehistoric curiosity. Many of the species found at La Brea disappeared altogether as the planet warmed at the end of the last ice age. The reasons for their demise are not yet fully understood, but may be especially pertinent to understanding the effects of climate change on animal populations today.

The tar pits have so many fossils precisely because of the tar, which one can still see bubbling to the surface in spots throughout Hancock Park. The gooey asphalt that trapped and entombed the animals turns out to be a great preservative. Thousands of perfect skulls and nearly complete skeletons representing more than 200 vertebrate species have been retrieved from the death trap.