I received a call today too and did not answer, no message left.  Any idea who this is?

Called the numberback - this is the Environmental Defense Fund.

This is the Environmental Defense Fund. If you'd like your number removed, simply call back and follow the simple prompts to do so. They will call from several different numbers, so it's best to remove yourself from their caller list rather than blocking whatever number calls you; trust me, I blocked 3 numbers from these guys only to get calls from several others. I like what they represent, but the continuous calls from various numbers gets really annoying. If I'm going to donate to your cause, I'll do so online and on my own time!

The REAL Environmental Defense Fund has an 800 number: 800-684-3322
There is no need to call the 661 number ... it may, or may not be theirs.
The REAL Environmental Defens Fund has an office In Sacramento CA ... the 661 area code is for Palmdale, not Sacramento.

Unknown caller - saved to my Contacts as Scam-8 so I know not to answer.