Your best resource is going to be the Sunset Western Garden Book, as it will break down growing conditions into very specific geographical areas and these can vary rather widely in terms of appropriate plantings, even by as little as a few miles. CA has probably the most diversity of growing situations of any state in the US :-) You may be in the 'high desert' area or a 'mild intermountain climate' but there's a vast difference between what will grow in one compared to the other.

Once you have determined what your Sunset zone is, you can review the list of hedging plants the book offers and make a choice based on these factors.

Temperature and snowfall are good things to know but an annual precipitation profile or guaranteed irrigation will really help identify the right hedging material for you.

In addition to Sunset look at what is growing in the vicinity already, in particular any native evergreen shrubs that might have potential.

If the lid is going to be off the tub much you may want to see if anything in the Sunset list of plants for use near swimming pools could work there.

Thanks very much. I'll grab the Sunset book and do some research.

Check this site for suggestions - almost at the bottom of the page they list 'best conifers for the hedges', in 2 different sizes/heights:
see here

Rina

I'm surprised no one was able to offer a more specific recommendation. Maybe you needed to post this on the California forum. On the California Zephyr, I remember seeing various evergreen manzanitas along the tracks as the train descended from the Donner Pass. Certainly, it seems like even up there I was seeing them by about 4000' feet. (I was following along with elevation using my GPS) Only issue with them is they might be a little too open, but I don't know how they behave in a garden if coddled and clipped.
Maybe call a nursery like Las Pilitas and see if they have suggestions for natives that would fit the bill. This one looks nice, they say it forms a good hedge. I doubt your hardiness zone is worse than zn 7.

Here is a link that might be useful: http://www.laspilitas.com/nature-of-california/plants/arctostaphylos-manzanita-x-densiflora-austin-griffiths-manzanita