Cal. Penal Code § 853.8

When a person signs a written promise to appear at the time and place specified in the written promise to appear and has not posted bail as provided in Section 853.6, the magistrate shall issue and have delivered for execution a warrant for his or her arrest within 20 days after his or her failure to appear as promised or within 20 days after his or her failure to appear after a lawfully granted continuance of his or her promise to appear.