Earthworks on steep, sandy/gravelly, south-facing slope in desert climate

I am working on a piece of property that has some unique challenges as well as advantages. The advantages include south-facing slope at just the right angle to take full advantage of the winter sun, well water, it's situated on the lower half of a hill, cold air moves off the property easily, and it has good drainage (too good, actually). The disadvantages include no cation exchange capacity (we'll be making massive amounts of compost), sandy/gravelly soil that goes down at least 75 feet, little rain (~11"/year), no water retention, and a steep slope (the property is 2/3 of an acre and has an elevation change of 32 feet from the top of the property to the bottom with the top half being the steepest). The top 1/3 is intended for orchard and poultry and it seems that terracing would be the best option to make the land workable, to retain water, to add organic matter, to prevent frost pockets, etc. But how stable would it be, particularly if we had a sizeable water event (I'm from Seattle, so this is relative in relation to the Boise area) or an earthquake, which is very infrequent but inevitable (the last one was in 1983). Also, how could we help minimize the damage from the hilltop above the property sliding down to this property (trees, shrubs, and herbaceous plants with taproots and fibrous roots planted along the top border come to mind). Would I need to terrace the entire area or just create terraced wells where the fruit trees are planted? Any ideas would be greatly appreciated.

Your land sounds similar to mine, except that I have aprox. 150 ft. of elevation change from bottom front to top of hill, and we get around 25" to 35" of rain in an average year. The approach I am using is terracing for both fruit trees and grape vines. These terraces will come off a switch backed path down the slope. I plan to make each terrace aprox. 10 feet in depth, that may have to change in some of the steeper areas, but that is the current plan of attack. Our house is on the ridge along with garden areas and currently growing fruit trees, passion fruit vines, etc. For limiting erosion I am planting crimson clover, Soft red winter wheat, oats, barley, triticale, and buckwheat. To retain water in the soil I am mulching and adding compost along with minerals. My soil is sandy loam about two feet deep.

Thanks for replying, Bryant. We have an extensive plant list of both fibrous and taprooted plants that we will use for soil stabilization. At the midpoint of the property a well was sunk and the gravelly sand continues for 75 feet down at that point. We will be making MASSIVE amounts of compost this year that we will have ready for use by spring. An agricultural structure consisting of a kitchen and root cellar with a Friendly Aquaponics greenhouse on top will be constructed this fall and winter into a section of the hillside. As the structure is being finished and covered with soil is when I feel the terracing or tree wells should be done (the orchard is directly upslope and adjacent to the structure), so I want to have the earthworks plan in place ASAP so that can be figured into the construction budget. Initially (if we do terraces), I'm thinking of having the terraces about 15 feet deep to allow for ease of movement around the trees. However, I see distinct advantages to maintaining the slope and excavating tree wells (about 15 feet in diameter) into the hillside which, of course, would be supported with retention walls. We would be able to set up sprinklers at the tops of the wells (essentially on top of the retaining walls) that would be set to water in a 270 degree arc along the slope and a tree well upslope from it. However, when frosts are an issue during bloom time, we could set the sprinklers to spray the tree tops of the trees downslope from them to prevent frost damage. We would also be able to dig a little deeper to fill the bottom of the tree wells with lots of incorporated compost, azomite, etc. and would be able to mulch heavily and have a suitable underplanting for the trees that we could fence off from the poultry. The slope would be planted with a poultry forage blend for the chickens and geese and we could control if or when the birds have access to the tree wells for pest control. Also, another reason to maintain as much of the slope as possible, the slope is south-facing and the angle is perfect to maximize the absorption of warmth from the winter sun. What do you think? By the way, Boise gets about 11 inches of rain a year.

What are these switch-backed paths you mentioned?

I agree with the idea of keeping the slope as much as possible. It sounds like you have a very good plan of attack to me, love the idea of an agricultural structure being part of the gardens, that will keep heating costs to a minimum.

The front of our property faces south, which is where I plan to do the terraces for the orchard and vineyard with vegetable gardens interspersed. Switch Backs are where you follow the natural slope, turning 180 degrees every time you reach the point of no return on a the hill/ mountain face. Almost all roads in mountains usually use this type of construction so water doesn't just rush straight down the mountain road and wash out everything at the bottom (Alpine road photos are easy to find on the internet, lots of them are used for the Tour de France.)

From the road our drive way curves up the hill for 400 feet, rising 150 feet in that distance, the road curves first to the left for 300 feet then the last 100 feet it curves to the right to arrive at the crest of the hill (a semi switch-back).

On our south slope this will make it easier to walk down and up the hill when tending the trees and vines. further but not as steep for the steps, being 63, I must think of the future and plan for working with the land instead of trying to change it. Our poultry is located at the top of the hill, as is our house and the goat house. I also have a north facing slope but that will be used for more of nature than for gardening or animal husbandry (deer, turkey, squirrel, and rabbits). We may add ducks or geese, or both to our list of meat animals, Wolf (my wife) has not decided yet. We are doing everything as we can, staying away from any long term payments is one of our requirements.