According to my iPhone, this number originates in Corte Madera.  I get this calls periodically and always at the most inopportune of times.  I called them back and I got a recorded message indicating the person on extension 1 was on the phone (probably bothering somebody else).  I have blocked them from my phone and hopefully will never hear from them again.  

Received a call from this number as well. Caller id said Larkspur.  There was noone on the line.

This number called me  claiming to be the IRS & that the tax return I filed from 2012-2013 was fraudulent. They tried to scare me by saying the police were coming to my house & I was going to be detained for 72 hours. This number is a scam. I contacted the IRS. Do not give this number any personal information & id recommend hanging up immediately