Help me out here guys. I want to give my 94 year old Father this rifle. He is a WW2 vet and sharp as a tack, and still drives. He trained on the carbine when he was serving in the Army Air Corp.

Nevada to Californication! Yes yes, I know how hard it is to move out, and I am one of the few that managed out of my family.
I have made millions dowsing for famous stars here in Nevada though, so I am NOT going back. Give a brother a hand----- can my Dad legally own
a M1 carbine in California?

Rifle - yes

Magazines are limited to 10 rounds, maximum.

Bayonet lugs are not a feature that makes a rifle an assault weapon.  That was the old Federal law, not California's law.

Still, do check the flow chart for compliance.

Here are the banned features:

Pistol grip
Thumbhole stock
Folding or telescoping stock
Grenade or flare launcher
Flash hider
Forward pistol grip

Why do we keep getting the bayonet lug thing repeated?  That was never a CA ban thing.  It WAS a federal ban item but that is long gone.

Anyway, as stated above the M1 carbine in unmodified form is gtg.  Usually.  No flash hider (there is a USGI clamp on FH).  No folding stock or pistol grip (M1A1 "paratrooper").

It's bad enough we hear it from out-of-staters but no Californian should be unfamiliar with the Ca. laws.  That suggests two things.  One is that you have restricted yourself more than the laws require, the other is that without familiarity with the laws, you may have crossed the line somehow and have an illegal configuration of some sort.

The standard carbine rifle is good to go. I had to get 10 round mags when I bought mine. Finding ammo might be an issue. I had trouble finding it during the panic. I haven't tried looking for .30 carbine in the local stores lately, but it looks like at least online sources are stocking it again.

This is a joke, right!

ATF publication 5300.5 is over 450 pages, it is all state Laws.  1/6 of that is CA. state and city ordinances. Even if YOU work for the CA. DOJ YOU don't know all the CA. laws.

Also to insinuate someone has crossed the line because they don't know all the codes when the OP was from NV

New ammo law after Jan 1 2018 which will double the price and also make all but the most common hard to find.

So be sure to include lots and lots of ammo.

After Jan 1 it will be against the law to bring it over the border except for small amounts for scheduled hunting.

For all those out there that think this is rocket science, it isn't.  Here's one of the many references one could use:

https://www.pewpewtactical.com/featureless-ar-15-rifle-grips-stocks-muzzle-devices/

Starting off, the M1 carbine is not a potential problem under federal laws, like barrel length or selective fire/full auto, etc.  If it is, then it's not as the OP described it.  It wasn't previously registered in Ca. as an assault weapon.  It's not one of the Ca. specific listed by name weapons.  Neither it's barrel length nor overall length are an issue.  Nor is it's caliber, it's not a ".50 BMG."  Magazine detachable?  Yes.  Mags must be 10 rounds or fewer.  But that wasn't the question.  Bullet button? Not if it's a standard M1 carbine.  

So, what are the features that define a featureless rifle? Does it have any of these?
   Pistol Grip - Nope.
   Thumbhole Stock - Nope.
   Folding/Telescoping Stock - Nope.
   Grenade Launcher or Flare Launcher - Nope.
   Flash Suppressor - Nope.
   Forward Pistol Grip - Nope.

It's a classic "featureless" rifle.  Now just for some clarity, for all you guys that keep wanting to bring up bayonet lugs.  A bayonet lug is not a factor in California.

Where could you get in trouble?  Friend at work was late in getting a build done before the beginning of the year. He has to go featureless now.  So what are the tricky, sort of, spots that might be a problem?  

Until just quite recently, the proposed regulations/definitions that go with the laws weren't available for review let alone finalized.  So what might be a "good thing" in the regs?  They have actually filled in some of the unclear (but not necessarily fixed all the lack of clarity) features carried over from existing laws.  This is good because when you draw a line in the law/regs, it is easy (or should be) to know where a feature, item, device, etc., is in when it comes to compliance.  Like barrel length - they describe how barrel length is to be measured.  Easy to enforce, easy to comply.  

Examples of an improvement. They defined, like it or not, and perhaps still not well enough, what would constitute "disassembly" when it comes to dealing with "fixed" magazines. They now specifically define a stock.  Before the question was out there as to whether a stock, like a Thordsen, might be described as a pistol grip.  The issue there is because a pistol grip (for California) is partially described by where the web of the hand (between thumb and forefinger) goes.  Now, "stock" is separately discussed and that's not an issue.  (Note that a Thordsen and similar stocks replace the pistol grip and original stock, so to speak.  There are still requirements in place covering certain types of grips and stocks to be observed.)

Still lacks clarity?  Flash suppressor.  They struggled with the definition last time around and it remains problematic.  

So where could the friend get in trouble?  Deleting the usual flash hider/suppressor and adding a brake that somehow triggers one of the Ca. factors.  Retaining a non-folding/non-telescoping stock and not addressing the "pistol grip."

So what might be an area that gets bandied about incorrectly?  Bayonet lugs - no need to restrict oneself from having a bayonet lug.