The Daniel Colvin – Mason Colvin connection: it does exist.
Back in January of 2011, I posted about trying to solve the riddle of the Daniel Colvin – Mason Colvin connection, noting that there was anecdotal evidence available but no documentation and that well-meaning but inexperienced researchers had tried to solve the riddle but in so doing had cited sources incorrectly, or used 2nd or 3rd sources; that their results were un–reproducible. This summer, (2013) I am happy to report, I found the proof I needed, in the form of an affidavit from Daniel Colvin’s Bounty Land warrant file which I downloaded from the Library of Virginia’s Bounty Land warrant database. And in that affidavit, given 3 May 1834, an 80-year-old Peter Triplett, a resident of Culpeper County, Virginia, explains not only how he knew of Daniel Colvin because he (Triplett) had served in the revolution with his son, Mason Colvin, but explains Mason’s equestrian accident soon after he and Mason were discharged. What struck Triplett as “improper” however, was the fact that both father and son were serving in the same war.
It’s the kind of first-hand, eye-witness testimony I was seeking because this is the source on which was based part of Louis A. Burgess’ claim in his Virginia Soldiers of 1776 that Daniel and Mason had served and Mason was subsequently injured after his discharge. But that claim didn’t explain why Daniel never turns up on the usual payrolls; that took some additional keyboard time to unravel why and what Daniel actually did do during his service tour – a tour to which Burgess only alluded. Citing the Triplett affidavit, claimed Burgess: “[Daniel] was enlisted by Capt. Benj. Roberts for Major Slaughter’s Battalion in Clarke’s expedition” But what that actually meant was that Daniel was part of a secret mission during the Revolution having to do with an expedition undertaken by Lt. Col. Gen. George Rogers Clark ( of Lewis and Clark fame,) in the winter of 1779 to roust the British from their forts in Vincennes, Illinois. Then -1st Gov. of Virginia, Patrick Henry, (of “Give me liberty or give me death!” fame,) wanted the mission kept secret, and Clark willingly obliged, and he put one of his first recruits, a Maj. Slaughter, in charge of raising a battalion of a whopping 350 Virginians (which turned out to be fewer owing to various fears and the strange secretiveness of the whole affair,) but with what he could raise by the winter of 1779, he marched to Illinois. That expedition is also known as Clark’s Conquest. 
As for Daniel’s connection to Mason, Triplett clears that up nicely:
[Triplett stated:] that he knew Mason Colvin in said service and [??] certified he was the son of Daniel Colvin who was also in the service a rare circumstance improper [in] his mind. That the said Mason Colvin and deponent were discharged at the same time and were [sent] home together.
Enroute home, Mason had a problem as they crossed the Allegheny mountains:
Somewhere in the Allegheny the said Mason got a fall from a horse or rather a horse fell on him by which he was much injured. That the said Mason lived several years after the war and then died and – he was the son of Daniel Colvin….
To date, little is known about Mason’s life – aside from his military service. Whom he married – if anyone — is also unknown. He is believed to have been born is 1764, and died (as has already been noted,) in the 1830s.
As to his father, Daniel, in 1934, a Mrs. Berkley G. Calfee, of Culpeper County, ordered a headstone for Daniel to be situated on her land in something in her application she called the “Colvin Burying ground.” In that application she noted that Daniel had served in “Slaughter’s detachment.” and that he died in 1790. Although the War department approved and shipped the engraved marble stone to Ms. Calfee, on her application, in the section identifying Capt. Ben. Roberts as the officer under who Daniel served, the quartermaster who approved the application did so after annotating the form in blood red marker:
“ No rolls on file.”
Yes, I could have told him that. Today the marble stone is located in what is known as the Masonic Cemetery in Culpeper County — N. Main St. (299) between Johnson and Hilltop Dr. —  but this same tombstone was earlier identified as being in the “Colven Graveyard” by Margaret Jefferies, a writer with the WPA who, in 1938 (4 years after Ms. Calfee had that headstone erected.) carefully noted Daniel’s stone as among some of the recent ones erected by the Culpeper D.A.R. Chapter. The cemetery was then private, located near an estate Jefferies identified as “Mt. Airy.” There is a separate WPA report on her survey of it. Then, mysteriously the same tombstone was relocated to Masonic. Why? Good question. In any event, someone at Find-a-Grave.com has built Daniel a nice memorial which features a picture of that headstone, and its current location, and also went to the trouble of ascribing to him a parentage which has yet to be confirmed in any documentation. In fact, dozens of letters to the War Department over the years from querying D.A.R applicants often received a form letter from officials which obligingly listed Daniel’s service tours and dates. But always, at the bottom of that list, was the notation, “no info on parents.” Even so, apparently the person who built Daniel’s Find-a-Grave memorial couldn’t resist giving him parents and so some names and dates were attached. But I would warn that attaching parents arbitrarily to Danial is worse than leaving that mystery unresolved for now.
Including Mason, Daniel’s remaining sons are believed to be: Nelson Colvin (1766-1834); Gabriel Colvin (1767-1833), and James Colvin (1768-1841) Daniel is believed to have married Elizabeth Magdalene Hansborough in Culpeper in 1763.
 A lengthy Wikipedia overview of the Illinois Campaign is available here. http://en.wikipedia.org/wiki/Illinois_campaign
 Curiously, there is no physical address for this cemetery. However, the ambitious will find it at GPS coordinates: 38.485186, -77.994207.