A lot of diving from Tucson is done in Mexico. San Carlos is about 5 hours drive south and has a lot of interesting stuff especially at San Pedro Nolasco island. Typical dive we see rays, Cortez angelfish, small spotted eels and at several divesites the seals come out to play. It's a rock substrate so you don't get the big coral formations like in Hawaii but it's still interesting diving. Most of the Phoenix and Tucson diveshops go there regularly, some even have bus/van service. There's several diveshops in San Carlos and lots of options for diveboats. If you're interested, Marina Terra is a good option for a place to stay, nice resort with a couple of pools, it's on the marina where all the boats leave from, and they have a beach club nearby.
Closer is Rocky Point/Puerto Penasco, I haven't been there in decades but there was some decent diving at Bird Island - a short distance offshore. Afaik there's only one diveop in Rocky Point now.
I'll probably get some heat for this, but I'm not currently planning to drive into Mexico anytime soon. There's a lot of drug cartel related activity across the border. Both Tucson and Phoenix also get their share of violence - mostly as the gangs battle it out.
[-]Around Tucson I think the only lake I'd try diving might be Patagonia Lake. But it could be really shallow now depending on the seasonal runoff. If the water levels are good, it's about 90' in places - otoh they rent paddle boats there also if that tells you anything. And it's at 4000' so it's elevation diving. BTW, even though Tucson (and Phoenix) are in the desert, the water is mountain fed so bring a wetsuit - it's cold even in the summer at depth. A friend mentioned that the visibility at Patagonia was terrible about 5 years ago, not sure if that's improved lately. I don't hear much about anyone diving there so maybe it hasn't.[/-] What Rob posted below...
The drive from central Tucson to Lake Pleasant would be about 2-1/2 hrs. depending on the time of day you pass through Phoenix - we have a lot of traffic and not enough freeways. It might be best to skirt Phoenix by connecting onto the 101 fwy. when you enter the Phoenix Metro area on I-10, it takes you within a few miles of the lake turnoff north of the city on I-17. There's a Sport Chalet at Happy Valley Rd. and I-17 that you'll pass about a mile north of the 101/I-17 interchange, you can rent tanks there on your way to the lake. Might want to reserve in advance if it's the weekend.
Only about 5-6 hrs. driving to San Diego from Tucson. Great diving in and around LaJolla Cove and Wreck Alley. There's really good shorediving off LaJolla.
btw, it's TuCson...lol