Three questions in one, but should be easy for a true cinema nut.

1) What was the last completely silent film commercially released in
the U.S.? And I don't mean one that started as a silent and had sound
added to make it competitive, and I don't mean faux silent films like
Mel Books.

2) Some years ago it was reported that a huge treasure trove of silent
films was found in Alaska. These were shorts and features that had
previously been either unknown or thought lost. What ever happened to
these films? Were they restored? Entered into a film archive? Made
available in some format?

3) Film restoration efforts are picking up speed; thankfully. However,
film lovers bemoan the many lost films, particularly films that were
reviewed favorably in the teens and 1920s. My question is this: What
is the "latest" lost film? That is, what is the most recent (close to
the present) film (or films) that has been destroyed or otherwise lost
that we will never have a chance to see again? (I'm wondering if there
are any features from the '60s onwards, particularly.).

Regarding the silent films unearthed in Alaska, this may interest you:

"In 1978, Dawson City was being rebuilt as a tourist destination
recreating its former self, a boomtown gripped by gold fever at the
turn of the last century. Excavating behind a former gambling den,
Diamond Tooth Gertie's, workmen struck archival gold, over 500 reels
of 35mm nitrate film from 1903-1929.

The Dawson Amateur Athletic Association started adding films to their
regular theater programs by 1903. But, Dawson City was the end of the
exhibition line and shipping was expensive. The studios didn't want
the films back anyway, in the days before revivals, tv and video. So,
the films were shelved in de facto cold storage in the basement of the
library. In 1929, an open air swimming pool that was flooded for
winter skating was going to be filled in permanently. Presumably, the
skating season was longer than the swimming season. All the films were
used as fill, dumped in, covered with dirt and boarded over.

The 510 reels discovered by the construction crew were in different
states of decomposition, and all were damp. The National Film Archive
of Canada rescued them, salvaged what they could, which came to about
425 reels, and began transferring the survivors to safety stock. 190
reels of US productions were transferred to the Library of Congress
for conservation."

http://www.moviediva.com/MD_root/reviewpages/MDRedskin.htm