This video shows a background reading of 30 to 40 cpm. From the manual the specifications of the geiger counter are known. It detects alpha, beta and gamma radiation with a pancake tube, however alpha radiation is blocked by air within 4cm and not detected. Assuming Cs-137, as most other detectors are calibrated against this source and the given tube characteristics, a dose rate of ~90 nSv/h is obtained. This is in perfect agreement with natural background radiation expectations.
Now taking the 150 cpm reading, you get 450 nSv/h. As you are not 24hours/365 days in this radiation field, it may considered safe, depending on your local legislation. However, this level is indeed above the background. This readings are out of the
error band and statistically significant. And the video shows a distance correlation to the the beach.
According to this article "Health officials respond to beach radiation scare" there is now an official investigation.
County health officials first learned of the radiation levels last week, and they sent their own inspector on Dec. 28 to Pacifica with a Geiger counter. Using a different unit, the county inspector measured the beach to have a radiation level of about 100 micro-REM per hour, or about five times the normal amount.
Note: 100 microRem/h=1 microSievert/h. So the original video even underestimated the radiation by a factor of 2.
Although the radiation levels were clearly higher than is typical, Peterson emphasized that it was still not unsafe for humans. A person would need to be exposed to 100 microREMs of radiation for 50,000 hours before it surpassed safety guidelines by the Occupational Safety and Health Administration, he explained.
100 microREM/h times 50 000 hours makes 5 REM or 50 mSv. This is outside of The 2007 Recommendations of the International Commission on Radiological Protection of 1 mSv artificial dose rate for common people. For the US special regulations apply. Your yearly combined dose should not exceed 5 mSv. Within 5 000 hours in a 100 micro REM radiadion field you get your yearly "save" dose.
So maybe you should avoid this confirmed hot spot beach West of San Mateo, south of Princeton Harbor. Or limit your visit to approx. 3 hours a day.
A recent Half Moon Bay Review article interprets the readings with the occurrence of radioactive Thorium in the black sand
“It’s not considered a radiation hazard, so long as you’re not eating it, and you’re not living on it, 24/7.”