Hi Dawn, welcome to the forum.
When you say garden are you talking about ornamental gardening as in landscaping or are you talking about vegetable gardening?
If it is landscaping then DITTO RBG - Xeriscaping is the way to go. When done properly it is drought tolerant, low maintenance, low water consumption and strikingly beautiful.
My Brother and SIL live in Erie, Co. Heavy, clay soil, little precipitation and strict water restrictions. After a failed attempt at traditional landscaping SIL opted for xeriscaping. She consulted with her County Agent, did a lot of research and hired a landscape contractor to assist her with the overall design. Brother and SIL did the installation. The result is a stunning landscape appropriate for a home with a view of the mountains.
Another option would be a Japanese style garden using drought tolerant plants. Japanese gardening is a minimalist approach. Less is best. Few plants are used and there is an emphasis on structure.
On to vegetable gardening. Because of your clay soil I see a sunken garden as a nightmare. You will have extremes. Either a water pit or a dry hole.
If you want to grow vegetables I would suggest raised beds. If you start small and use an intensive gardening method such as SFG you can grow a lot of herbs and vegetables in one or two 4' x 4' boxes. Water your vegetables early in the morning with either a bucket of water and a cup or a watering can. No over head watering. Water only the base of the plants. Another option is container gardening. I find container gardening to be more expensive and more work than SFG.
Anyway - that's my 2 cents.
BTW - SIL wanted a vegetable/herb garden so Brother built 2 4' x 4' boxes with legs to create table height gardens. They are situated on their deck which has direct access to the kitchen. SIL is an excellent home cook and loves having fresh vegetables and herbs within easy reach.