If the soil remains reasonably moist, then your choices expand :-) Azaleas generally need a fair bit of sun to bloom well so they may not be the best choice but the skimmia and hostas will be fine. Skimmias absolutely NEED shade and like it moist. You can also add ferns (like our western sword fern), sweet box (Sarcococca sp.) and any other shade loving perennials. Another good choice would be Mahonia or one of the dwarf huckleberries (Vaccinium ovatum Scarlet Ovation or 'Thunderbird' or Vaccinium moupinense). Just be aware that the soil will probably be very rooty, making it hard to dig large planting holes. My suggestion for this type of situation is start with small plants. Easier to dig the holes and smaller plants will establish easier and faster with the inevitable root competition.

Do all the plants need to be salt tolerant or only some? Does the tolerance include foliage and airborne spray, or roots and salty runoff, or both? Plants don’t make much of a difference to sound levels; only something solid like a wall or solid fence can do that. Plants can provide visual screening, however, and if planted on a berm, the berm can provide some sound blocking or reflection. Most of what grows that is native in zone 4 isn’t evergreen except for conifers, and not many of them are salt tolerant IME. You could also try growing from cuttings if other folks you know would let you, although it wouldn’t have genetic diversity unless you took cuttings from different shrubs and trees within species. Just so you know, Rosa rugosa isn’t native or evergreen, though it has naturalized over a fair amount of the Northeast. There are native roses such as R. palustris AKA swamp rose and R. virginiana. For evergreens, balsam fir as it grows on my property is relatively narrow, but as with most of these plants, I don’t know about salt tolerance. Check out junipers as another hardy needled evergreen that may have some salt tolerance. I can grow Rhododendron maximum, but it does get winter foliage damage in sun. My mountain laurel AKA Kalmia latifolia Seem to do better with keeping their winter foliage looking nice, but are mostly in at least part shade, so that might be the explanation. I don’t think either is salt tolerant. Yew tend to be eaten by deer if they are an issue for your site, and often Thuja are eaten into lollipops as well, with all foliage missing as high as the deer can reach, so you may want to set up protection for them this fall, either netting on posts or a webbing of posts and high test fishing line which they have difficulty seeing. For deciduous plants, look into the native Viburnums, some of which should be hardy enough for you, but I don’t know about salt tolerance. Physocarpus AKA ninebark isn’t evergreen, but it is densely twiggy and so provides fairly good visual screening and is a US native. Hydrangea arborescens is native, but in my garden doesn’t get taller than 4’-5’ and prefers shade in the afternoon. I have seen Amelanchier AKA shadblow or serviceberry growing in the median strip of the interstate, so it must be at least slightly salt tolerant. There are several deciduous dogwood shrubs and Ilex verticillata AKA winterberry holly that have winter interest. If you are looking for an inexpensive source of seedlings so you don’t have to grow your own, check out the NH state Nursery. Order early next season (check in January) since I think that they may be done shipping for this year and they often sell out of popular plants. Many, though not all, are native plants.

Addison, I have no personal experience growing jack pines, because I have no areas with salt, and almost no sandy soil anywhere on my land. I live on a dirt road which never receives road salt, and the areas I'm re-foresting are a good distance from that road, behind the house. I mentioned jack pines because they seem to grow profusely in coastal areas in Maine and MA where the soil contains a good proportion of sand and salt. It does seem they grow quite large and would indeed be unsuitable for your hedge, but perhaps will grow on the ridge as you've planned. I just don't know how they do in areas with rich, un-salty soil. I like trees and shrubs to look natural as well. I never prune anything on the property, except to remove branches that are growing into our walking trails or into the path of the mower. However I don't worry much about whether a shrub or tree is native. My apples, crabapples, and lilacs (some of both are in my front yard along the road) are not native, but I doubt that the sight of these ruins whatever Vermont experience visitors might expect. Too bad for them, if so, because these trees/shrubs are ubiquitous all over the state, and impossible to avoid!

I plant a mix of plants from all regions of the world. I have many natives but also many that are not. The wildlife and insect populations seem to flourish and I notice just as many birds nests, insects feeding, etc on most of the non-natives. That is not an attempt to get you to change your mind, just fyi. And also fyi, Pacific wax myrtle (Myrica californica) is an extremely vigorous shrub that fairly quickly grows to 10-12' tall and 10-12' wide. Most narrow plants are going to be cultivars. And there are just not that many cultivars of native CA woody plants, more's the pity. And you are essentially looking at plants that are native to your area, which means an even smaller selection. One of the problems with native plants in CA is that our climate varies so much; what is native a few miles away from me (coast redwood) does not do particularly well where I am, for example. If I plant them, I have to provide a lot of supplemental water. So much to learn...mostly by making mistakes the first time!