A shelter in place order was lifted Friday afternoon for the area near Everest Public High School in North Fair Oaks after a chemical found earlier in the day was deemed not to be hazardous.
Residents can resume normal activities, the San Mateo County Sheriff's Office said about 1:40 p.m. on social media.
Authorities didn't say what was found; a deputy with the San Mateo County Sheriff's Office discovered the material while walking in the area Friday morning.
The sheriff's office posted on Twitter about the discovery shortly after 11 a.m. and the area was closed. Nearby residents were asked to shelter in place while the sheriff's office investigated along with the Menlo Park Fire District and the San Mateo County hazardous materials team.