Help! What do I do with clay soil?

[feminazi]

My backyard is a mess. The grass is splotchy and the soil has so much clay that in winter it turns into a swamp from the rains and lack of sun (northern California) and in summer it bakes to a hardness that I swear rivals concrete.

It's not a large plot of land and my plan was to leave grass in the middle of the yard (probably lay topsoil and some sod for that at some point since the current "grass" is so weedy) and remove the grass from the edges so I can replace it with a border of small stones or bark nuggets and container plants. That means digging up the grass/soil on the perimeter of the yard to get rid of it.

I spent last Sunday on the area that abuts the house. It took me hours to remove the grass clumps and less than an inch of clay from an area about 3'x20'. The soil is way too hard to get a shovel under to remove large chunks at a time. Wetting it with the hose just turns it to muck. I had to use a hoe and chop-chop-chop. Not a lot of fun.

I thought about getting a rototiller, but I have underground sprinklers and am afraid of hitting them. I have no idea how far down they are since the sprinkers were there when I bought the place.

Can any of you offer any advice? I'm thinking I may just have to "hoe" off the grass and a little clay and build on top of that instead of trying to recess it a few inches.