You might want to check with the youth agencies in Arizona about your specific circumstances, but generally your parents are responsible for you being safely and adequately provided for until the age of 18.
This doesn't necessarily mean that they must allow you to live in their home, but it does mean that they can't unreasonably deprive you of the basic necessities of life.
You may be entitled to financial assistance from your parents if they are unwilling to allow you to return home. You are almost certainly legally entitled to retrieve some of your belongings (such as clothing and other basic items) whether or not you paid for them.
However, it sounds to me like the most useful avenue you could pursue at the moment is mediation with your parents. Realise that while it may be possible for you, your girlfriend, and you child to get by without their support and assistance, your life is going to be considerably easier if you are not at odds with them.
You have a whole lot of difficult decisions to make in the coming months, and the more support you have from family and friends the more options you'll have.
I watch my 18 year old daughter struggle with the challenges of teen parenthood every day, and I think that she'd be the first one to say that even though she thought she had it all worked out, the realities of parenthood are far more demanding than she'd ever envisaged.
You don't mention how long ago your parents kicked you out. If this has only happened in the last few days, then you and they probably both need some time to cool off before the situation escalates. While that's happening, you might want to think about the kinds of support you'll need over the next couple of years and where your parents fit into that.
The clearer you are about what help you'd like from your parents, and the clearer they are about what support they will and will not provide, the more able you'll be to start putting in place the network of resources your new family is going to need.