need a drought tolerant tree species

I am looking for ideas for the best species of trees to grow in succulent gardens in warm, arid climates. The qualifications, other than drought tolerance, are: not overly dirty, no heavy periods of leaf drop (or relatively dinky leaves) but still provide filtered shade over a relatively large area.

How about something like madrone or manzanita? They're much neater than most of the other drought tolerant trees I can think of plus they're native. Geijera parviflora isn't native but I see it a lot up here and it might work too. It does have berries but I think they get eaten for the most part rather than dropping on the ground. Or if you can live with something deciduous (but with small leaves) Chilopsis linearis is one of my favorites.

Had not thought of Madrones or Manzanitas... I have trouble growing either- not sure if I over or underwater them. Have yet to get one to even live a year.

I've had the best luck with them if I plant them in late fall/early winter, then they get the winter rains and don't need much water after that (I water my CA natives bed about every 3 wks during the summer, but I think they could get by on even less than that if they had to). I'm also not sure how they do where you are--I just checked Calflora to see where they grow naturally and madrone is only found in the coastal counties in SoCal and not farther inland. I'm not sure how far inland Tarzana is but that might be the problem.

it gets pretty baking hot here (120F sometimes)... we're about 10 miles inland, but the San Gabriel mountains are inbetween so heat sits here and goes no where.

Maybe those won't work for you then--they do fine where I am and we usually have at least a couple heat waves every year where we get around 110, but looking at the distribution that Calflora shows, they do grow farther inland up here but in SoCal look like they're only on the coast. That's a shame, they're very nice trees and would have fit your requirements. The Chilopsis should still do fine if you don't mind it dropping its leaves in the fall (other than that I don't find mine to be very messy) Most of the other things I can think of like palo verde's tend to be messy.

I was wondering about Palo Verdes... The shade is almost insignficant, but I was concerned they, like some Acacias, would be really messy. Not sure there is a perfect tree (except a palm tree of course)

I would have suggested palms but figured you'd probably already thought of those :-) I'm not sure how palo verde's compare to acacias...I think if you keep them watered a little bit then they are a bit less messy than they would be otherwise, but I know they have a reputation for being messy.

Here are some other possibilities to check out--if you don't like these there are lots of other possibilities on this website. I think it's written for Arizona, but I imagine a lot of the things they list would do well for you too (and they list Sunset zones for many of their plants along with the USDA zones so it's easier to figure out what might really do well for you)
http://www.desert-tropicals.com/Plants/Casuarinaceae/Casuarina_cunninghamiana.html
http://www.desert-tropicals.com/Plants/Boraginaceae/Cordia_boissieri.html
http://www.desert-tropicals.com/Plants/Anacardiaceae/Pistacia_lentiscus.html
http://www.desert-tropicals.com/Plants/Fabaceae/Sophora_secundiflora.html

thanks.. some excellent and not anticipated suggestions!!

The Texas Mountain Laurel, Sophora secundiflora is absolutely gorgeous in bloom. The fragrance is somewhat like Grape Kool-Aid. It is very slow growing so you would need to get the largest specimen you could find. It is a small tree and the shade would be somewhat dense.

Cordia boissieri, Texas Olive Tree, is also an attention grabber in bloom when the tree is covered in clusters of white blooms with yellow centers. Hummers and butterflies are attracted to the flowers. The tree is somewhat slow, although, not as slow as the Texas Mountain Laurel. If the top is killed by a heavy freeze, it will return from the roots.

I know of a tree that fits all your qualifications. It is very drought tolerant, not overly dirty and it provides excellent filtered shade over a large area once it reaches maturity. Since it is a Legume its nitrogen fixing nodes allow other plants to thrive underneath as this photo shows.
http://info-poland.buffalo.edu/classroom/PM/mes.jpg
My DH thinks I'm crazy to recommend this tree. I love its lime green colored leaves in the spring which mature to a dark green. It's a Honey Mesquite, Prosopis juliflora.

thanks for the suggestions... how 'dirty' all these trees? I know all trees shed leaves, but some shed all at once, while others shed year round. The all at once shedding has the advantage of having to only clean the leaves out of the cacti once a year... but it can smother the plants if its a heavy shed, or trap enough moisture that it allows rot to occur... which is why itty bitty leaves are an advantage here. But on the other hand ,really large leaves are easier to pull out of cactus and less 'messy' in the long run. But they also trap more moisture around the base of the plants if not removed right away and really cause problems that way.