Personal Notarized letters?

Do they hold any value when trying to prove you've been in the country for the DACA?!

What I mean by that is if a family member writes a letter claiming they're a witness to you being in the country, and then they notarize it, can that be used among other documents when filing for the deferred action in California?

Yes, you can use notarized letters. However, they don't hold as much weight as actual proof from the time period specified by USCIS. I sent one proving I was present in the country on June 15, 2012, but I included other pieces of evidence including call records for my cell phone.

They are called Affidavits, and yes, USCIS will accept them for certain requirements.

Q1: May I file affidavits as proof that I meet the guidelines for consideration of deferred action for childhood arrivals?
A1: Affidavits generally will not be sufficient on their own to demonstrate that you meet the guidelines for USCIS to consider you for deferred action for childhood arrivals.
However, affidavits may be used to support meeting the following guidelines only if the documentary evidence available to you is insufficient or lacking:

• A gap in the documentation demonstrating that you meet the five year continuous residence requirement; and
  
• A shortcoming in documentation with respect to the brief, casual and innocent departures during the five years of required continuous presence.

If you submit affidavits related to the above criteria, you must submit two or more affidavits, sworn to or affirmed by people other than yourself, who have direct personal knowledge of the events and circumstances. Should USCIS determine that the affidavits are insufficient to overcome the unavailability or the lack of documentary evidence with respect to either of these guidelines, it will issue a Request for Evidence, indicating that further evidence must be submitted to demonstrate that you meet these guidelines.

USCIS will not accept affidavits as proof of satisfying the following guidelines:

• You are currently in school, have graduated or obtained a certificate of completion from high school, have obtained a general education development certificate, or are an honorably discharged veteran from the Coast Guard or Armed Forces of the United States;
• You were physically present in the United States on June 15, 2012;
• You came to the United States before reaching your 16th birthday;
• You were under the age of 31 on June 15, 2012; and
• Your criminal history, if applicable.

If the only evidence you submit to demonstrate you meet any of the above guidelines is an affidavit, USCIS will issue a Request for Evidence, indicating that you have not demonstrated that you meet these guidelines and that you must do so in order to demonstrate that you meet that guideline

u need to gather notorized letters from long time best friends, ex co-worker that can say you worked with them