I live in northern California and don't have really cold weather like many of you have. I manage to keep warm everywhere but my ears. What do you use that will allow me to wear my helmet and keep my ears covered ?

Something like this. Same issue here in SoCal, usually not cold enough to really bundle up, it's just nice to get the wind off of my ears. I couldn't find the exact ones I bought on Amazon-- which were super cheap, a 3-pack for about $15. I tend to wear it like Pic #3 , so I can pull it up over my mouth for descents.

search men's fleece headband ear warmer

I love my tube scarf! On a recommendation here on BF, I got one of the Buff brand. It is lightweight merino wool, which means it is comfortable in a very wide range of temperatures. The pictures above show the various ways to use one.

I also have a merino wool cycling cap with ear flaps. This morning's ride had 34°F weather with high wind. I pulled down my ear flaps and wore the scarf like the third picture except that I also had it around my jaw. My jaw gets cold easily. With this setup, I was perfectly comfortable.

Wear a hoody.

no doubt. buffs are a must. just the thin performance fabric

can wear as a hat with ventilation in the top too

https://www.amazon.com/SUGOi-92911U-.../dp/B005BYYKBA

I've got a Sugoi ear warmer headband that I'm happy with (link above). I also have a tube scarf, which is much more versatile.

I've tried Belgian style winter caps, tube scarfs/buffs, etc. All either left ear lobes exposed or fell down while riding.

The only thing which worked for me is the Giro Ambient cap. It covers my entire ear and stays there the whole ride.

https://www.giro.com/us_en/ambient-skull-cap.html

Something like this works for me down to about 40F. Wool cap with earflaps goes from there down to about 25F:
https://www.walzcaps.com/collections...ap-cycling-cap
A buff works in the same temperature range, and perhaps a bit colder, but I just haven't taken to the buff as I have to the cap with ear flap.

Below that, a balaclava (though this may not apply to SoCal!).

I like these. (They also come in a heavier fleece, & additional colors although I prefer black.) Easy on/off with velcro.
www.amazon.com/dp/B00PCT637I/ref=cm_sw_r_em_apa_i_ztRcCbSQTDVJH

Wind block throughout, thin but warm? (not much room under my only helmet)

Depending on what you mean by cold ears. I only feel the cold air going inside my ears. So I cut a toilet tissue in half and stuff it in my ear. I can hear but it shields the wind from going inside.

As far as outer ear, no problem so I'd never need muffs.

I just wear an ear band. I put it on my neck, then the helmet and pull it up over the straps. That way I can pull it down later in the ride when I warm up without stopping to pull off the helmet.

Around here I can usually find one in the street over the course of a winter or get one out of any elementary school lost & found. So Cal you may actually have to buy one.

https://www.rei.com/product/103631/r...fleece-earband

What are "buffs"?

'Enthusiasts', is one definition..

neck gaiter is another term

The OP needs a cap which covers his ears, that's all.

The OP doesn't need multiple layers, ski helmets, scarves or toilet paper shoved inside his ears.

He needs a hat which covers his ear, that's all.

"That's all" is what you say, not the OP. Others have provided practical solutions to the OP's cold ears.

Giro Ambient Headband. $20.

Wore one this morning on a 39F NorCal morning. It was perfect.

I wear a Halo headband. When it's nippy, but not cold enough for my balaclava, I'll pull the head band down over my ears.

Giro Ambient products are really nice. The OP can't go wrong with this.

Yep. The only drawback is that it's small and black and tends to get lost in the transition from laundry basket to dresser.

I'm trying not to buy anything else black. I often toss things in my bag, and when there is more than one black thing, I can't tell the things apart. I have even taken to coloring things (not clothes) because of this problem.

I have a Pearl iZUMi Headband

this one seems to be a newer version. well worth $20

they also make a "thermal" version that I have not tried

I use a pair of size XXXS toe covers, one per ear. If I'm going into town and need to dress it up, I'll wear a matching Giro Ambient headband over that.

https://www.tredz.co.uk/.Giro-Ambien...over_94019.htm