In March 1970, Joseph Alioto, who was serving as the Mayor of San Francisco, took a significant step by issuing a proclamation for the observance of Earth Day. The proclamation aimed to mobilize citizens around environmental issues, generating awareness and action concerning pollution and conservation. This was a pivotal time in American history, as the 1960s and early 1970s were marked by growing concerns around environmental degradation and the public's increasing involvement in ecological activism. The event was part of a broader movement that sought to establish environmental protection as a national priority.

The first observance of Earth Day was later celebrated on April 22, 1970, garnering massive participation from people across the United States. The Mayor’s proclamation was an important precursor, as it served to institutionalize the movement within a key urban center known for its progressive values and activism. San Francisco's urban landscape and diverse population created a conducive environment for discussions about ecological issues, making it a fitting location for such a proclamation.

This act was not merely ceremonial; it was an integral component of the larger Earth Day initiative that sought to advocate for clean air, water, and natural resources. Following the proclamation, many events and activities were organized, both locally and nationally, signifying a corresponding resonance among many Americans who were increasingly concerned about their environment. The groundwork laid by such proclamations paved the way for the environmental legislation of the following decades, including the establishment of the Environmental Protection Agency in December 1970 and the subsequent Clean Air Act and Clean Water Act. Joseph Alioto's leadership in this movement captured an essential moment in the emergence of environmental awareness across the nation.