Coniferous needles are no more acidic than other leaves.

pH

A pH between 5.5 and 8.5 is optimal for compost microorganisms. As bacteria and fungi digest organic matter, they release organic acids. In the early stages of composting, these acids often accumulate. The resulting drop in pH encourages the growth of fungi and the breakdown of lignin and cellulose. Usually the organic acids become further broken down during the composting process. If the system becomes anaerobic, however, acid accumulation can lower the pH to 4.5, severely limiting microbial activity. In such cases, aeration usually is sufficient to return the compost pH to acceptable ranges.

Here is a link that might be useful: Compost Chemistry

AND the composting process tends to bring all the materials toward neutral pH anyway. So compost away, and happy rotting!

Pine needles, when bruised and soaked in distilled water for at least 24 hours will test at about 3.5 pH but when composted the finished compost will be near 7.0 or neutral. That soil may be acidic, not because of the pines or needles but because the soil Calcium or Magnesium has been washed out by the rains that may have fallen. Sand, without adequate levels of organic matter, tends not to hold any nutrients very well.

Since I am cutting quite a few trees to create a build site, I will have a large pile of chipped up pine branches, needles, weeds. Will try to get as much as horse manure (probably fresh) from neighbors to mix in with the pile too. But as we are heading into the dry seasons here in California, this pile will not get to stay wet. Being dry, how long would it take to become usable compost?

This pile will be the foundation of my new compost for the next few years.

If you have large equipment coming in, you should take advantage of it, already dig the vegetable beds and bury the trunks there. In the future, the water retention of those beds will be much better. I don't think a log belongs in the compost pile. You might consider injecting the logs with edible mushrooms for a secondary, totally free harvest. Phoenix Oyster is indicated for conifers.

The branches and needles, shredded and mixed with manure, can form the proper pile, though things will work just as well if you place all of it on top of the beds. Assuming you make a pile, it will help if you place it in shade, but the occasional hosing will keep it going through the summer.

If the tree shreddings are fresh, and the manure is fresh and urine-soaked it won't take long to get finished compost out of a pile.

Can I accelerate pine needle (acid) composting by mixing with wood ash (base) and keeping the mixture moist?

If you use pine needles...compost to finish. This is very important if you're worried about pH.

You can compost almost anything on the pH scale and eventually get it at/near neutral, but you have to finish the process.

Thanks to high lignin, wax, and cellulose content, this can take a while in some environments.

Pine bark is rather pH neutral on it's own...broken down or not.

Conrad, there is no good reason to mix wood ash with pine needles when you are composting them, or even when adding them to your soil because those pine needles will not significantly change your soils pH . The wood ash will change your soils pH, for a short time, if that soil needs a pH change.

Here is a link that might be useful: pine needle pH