Sts. & Hy. Code, § 5876

When the superintendent of streets finds that sidewalks or curbs have been constructed, or that their construction has been guaranteed to his satisfaction, in front of properties constituting more than fifty percent (50%) of the frontage in any block, or where a petition signed by the owners of more than sixty percent (60%) of the front footage of the block has been filed with the city clerk requesting the installation of such improvements, or where a petition signed by the owners of more than sixty percent (60%) of the front footage of any part of an unimproved portion or portions of a block has been filed with the city clerk requesting the installation of such improvements in front of said part, or whenever the legislative body of the city upon its own motion has ordered the installation of such improvements in front of said part, said superintendent of streets may, and upon the instructions of the legislative body of the city shall, notify the owner or person in possession of the property fronting on that portion of the street in such block in which no sidewalks or curbs have been constructed theretofore, to construct or cause to be constructed sidewalks or curbs in front of his property.