Suppose we take a very long, very high valley, in the high Sierra or southern cascade range and heat the sides of the valley near the top during the coldest winter months. This melts the snow pack, causing it to flow as water down the valley, where it refreezes as ice due to the natural weather condition. The ice that forms would then melt slower than the snow pack naturally would and could potentially be made to form an artificial glacier that survives through the summer and be built larger and larger over several years. It may be more effective/efficient to use a heat pump system to draw heat from the area of soil (or a special type of dam) intended as the start point for the glacier formation and release the heat in the melt area, but this is considerably difficult given the scale. If glacier establishment is successful than this heat pumping stops being necessary and can be shut off as the glacier would keep the ground beneath it cool year round. This is a relatively efficient method of forming a longer term strategic water reserve for the State of California. A significant power source is required to melt the snow pack. Nuclear power is likely to be best for the harsh conditions, with special seismic resistance redundancies (build it inside a mountain) and one of the newer self-regulating technologies.
The geography has to be right to make this work among other factors. Possibly, it is an idea worth looking into.
The Sonora pass which Highway 108 follows could be an acceptable location for the formation of artificial glaciers. A feasible experiment could be conducted in which the highway is kept clear for part of the winter and open for vehicles participating in the experiment. After the first heavy snowfalls of the winter, heavy equipment can be used to clear the road and then construct a few large snow piles or stupas near the road. These snow piles will continue to grow and compress during the winter as a result of additional natural snow fall. Then the stupas can be measured and monitored throughout the warmer months as soon as the highway is reopened. This method could be used to demonstrate the feasibility of preserving artificial ice in the test areas over the summer, and may even successfully demonstrate the creation of artificial glaciers by seeding. Success in this location would mean that the process could be repeated further north and could be provide additional strength to more of the San joaquin water systems.
Once an artificial glacier is established, it will cool the area and will help to insure high snow precipitation in the winter. This is the opposite effect of standard reservoirs which actually cool the area in the hottest months of summer but warm the area in the coldest months of winter. Standard reservoirs are a tried and true means to store water in regions which rely on meltwater, and they can be designed to provide more water on demand. Glacier water storage does not provide on demand water, but instead just melts at a predictable rate throughout the summer and as such, must be used in conjunction with reservoirs. A glacier fed reservoir has a constant input flow of water during the summer, which allows the reservoirs to supply more water during the driest months.