Pet Rocks were a 1970s fad

FAD

In biochemistry, flavin adenine dinucleotide is a redox cofactor involved in several important reactions in metabolism. FAD can exist in two different redox states, which it converts between by accepting or donating electrons. The molecule consists of a riboflavin moiety bound to the phosphate...

 conceived in Los Gatos, California

Los Gatos, California

The Town of Los Gatos is an incorporated town in Santa Clara County, California, United States. The population was 29,413 at the 2010 census. It is located in the San Francisco Bay Area at the southwest corner of San Jose in the foothills of the Santa Cruz Mountains...

 by advertising executive Gary Dahl.
In April 1975, Dahl was in a bar (which is now Beauregard Vineyards Tasting room in Bonny Doon

Bonny Doon, California

Bonny Doon is a census-designated place in Santa Cruz County, California. Bonny Doon sits at an elevation of . The 2010 United States census reported Bonny Doon's population was 2,678....

) listening to his friends complain about their pet

Pet

A pet is a household animal kept for companionship and a person's enjoyment, as opposed to wild animals or to livestock, laboratory animals, working animals or sport animals, which are kept for economic or productive reasons. The most popular pets are noted for their loyal or playful...

s. This gave him the idea for the perfect "pet": a rock

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

. A rock would not need to be fed, walked, bathed, groomed and would not die, become sick, or be disobedient.