The Corps of Discovery Expedition has become one of my primary areas of focus. I've actually completed the entire Western route and most of the Eastern return routes by truck, foot, and raft, and (while unrelated to L&C) found a gravesite of a member of one of the Fremont expeditions and went through the process of informing the Center for the American West and a historic society in the Colorado county it's located in, which could be relevant to suggesting potential resources to help determine the validity of this engraving.

A broad answer to your question is that historians, tribal land managers, DOI employees, and others are still finding and uncovering bits and pieces of history from explorers, trappers, and other non-tribal expeditions from the pre-Western settlement / expansion period. Not everything is marked, much remains unfound (and could in perpetuity).

The first part of your question - "is there a chance that this is legit"

Given that the engraving is specifically for William Clark (and some other significant factors), it could absolutely be legit.

The unified expedition party kept a course well-North of the Yellowstone River while traversing Montana on their Western journey in the Spring / Summer of 1805. However, on the return journey, Lewis and Clark actually split into two parties on July 3rd, 1806, at Traveller's Rest (now a National Historic Landmark, just about a mile outside of what's today Lolo, MT). Clark took his party South up the Bitterroot River, which they referred to then as both Clark's River (it's a tributary of the Clark's Fork) and the "flat head river."

From the time he reached the mainstem of the Yellowstone until the two parties rejoined on August 12, 1806 (at a spot about 5.5 miles South of present Sanish, ND) Clark maintained his route consistently right along the Yellowstone River, leading him right through the exact area you've found this carving at - Billings MT.

On July 25th, 1806, Clark made his famous engraving on Pompeys Pillar, about 30 miles Northeast of Billings / your location in question.

Referring to Clark's personal diary of the expedition, particularly the few days preceding July 25th (an estimate of when he'd have been approaching and passing through present day Billings), I've refreshed my memory on the following:

On July 23, Clark and his party camped near the Clark's Fork of the Yellowstone River, about 15 river miles Southwest of Billings. On July 24th Clark entered in his daily-kept "Course Distance & remarks July 24 1806" as passing a tributary of the Yellowstone he called 'brook' which was determined to be Bitter Creek, just opposite of present day Billings, and in his diary Clark notes camping at "Pryers River" (present day Dry Creek) just above (Northeast) present day Billings. This is from Gary Moulton's edits on the location of the July 24 camp: "The camp of July 24 was just below the mouth of Dry Creek and on the opposite side of the river in Yellowstone County."

So, if your picture is of a legitimate William Clark carving, and this is within the precise 1-5 miles of river Northeast of Billings (of the 7,000+ mile trail completed by L&C between Oregon to Missouri), it actually had to have been inscribed on July 24th based on Clark's own travel log, atlas, and journal.

I find it very interesting (and rather convincing, when it comes to considering the legitimacy of it) that Clark was at the location of your engraving in question the very day before he made the most famous engraving from the entire expedition. However, nothing is written in Clark's diary or Moulton's edits about an engraving on this day in this location, and he does note engraving his name & the date the next day at Pompeys Pillar (he also notes the extravagance of that geological formation, it's view, and the loads of native engravings of animals and scenery in the rock as well, as he was clearly smitten by its beauty).

As far as comparing this potential Clark engraving to the very well-known engraving he made on July 25th at Pompeys Pillar there are some notable similarities, particularly in the cursive "Cla", and the fact that he follows a large capital "W" with a smaller capital "M" for his first name. The style of these two capital letters do indeed differ between the two engravings, as well as the location of the smaller capital "M," but that could have to do with the carving tool used or the sediment/medium being carved in.

Perhaps the most significant factor in all of this is the distinguishable "July 24" in the engraving you photographed - with the "24" and the downward swoop of the "J" in particular being quite clear, the latter closely matching his Pompeys Pillar engraving style of the date "July 25 1806" he included directly below his name.

The second part of your question: "why isn't it publicised more?"

I would say that the lack of a diary entry mentioning this engraving, distinguishing it from the citable recorded history of his famous engraving the next day at Pompeys Pillar, is the primary reason this isn't publicized more. It's important to remember that unless one of the four primary journal-keepers on the expedition (Lewis, Clark, Ordway, or Gass) took note of it, there weren't any other English-speaking or literate people around to offer an accounting of what happened (with the exception of the occasional scout/trapper/trader they ran into - most of whom they already knew). Additionally, it wasn't until 1877 when the Billings area was settled by folks from the Gallatin area, who formed Coulson, effectively the first actual town in the Yellowstone Valley. Thus, there is a significant 70+ year gap in the historic record of the area (with the exception of the remaining tribal oral history, and the scant accounts from a handful of less-renowned trapping or charting expeditions) between the L&C's first charted expedition through the region and it's actual settlement.

In short, unless the members of the L&C expedition jotted down these unsubstantial happenings (like the engraving of names), there really is no substantive record of any kind available for historians to jump into to validate or investigate things like this. With the exception of a few small secondary facts, the information catalogued by a few expedition party members is a pretty exhaustive record.

I too was unable to find any confirmation on the validity of this potential historic cite online, but I would highly recommend contacting Billings municipal offices (land use & planning, or parks & rec) or Yellowstone County (depending on the urban growth / city boundary) to ask about the lock & key cordoning off the area. They'll likely be able to give you information on why it was protected, to determine if it was anything more than simple prevention of further vandalism.

In conclusion, I think it's always safe to start by pointing out that this, unfortunately, could be the handiwork of a very thoughtful, detailed, and historically-aware 19th century vandal who made the engraving over 100 years ago (based on the weathering of the stone).

However, taking into account (1) your saying this was found just North of Billings, (2) that being precisely where Clark and his party were on July 24, (3) the discernible "July 24" (or, at least the "J" and the "24"), (4) the notable similarities in this engraving with the famous one on Pompeys Pillar, and (5) the circumstantial evidence of this engraving having to have taken place the very evening before Clark made the most famous name engraving of the entire trans-continental expedition, I think there's a reasonable probability that this is indeed legitimate.

Thanks for a great question like this! It really makes history come alive, and stimulated fun look back at my research and experience along the route of this amazing expedition (albeit with the modern comforts of occasional wifi, GPS, beer, and a fly rod).

Sources: Meriwether Lewis, William Clark, John Ordway, and Patrick Gass (the latter two being expedition members) maintained thorough daily journals, atlases, and records of the expedition. They are all available for free online here, in the original language they used, and modernized translations (even taking into account temporal differences in written English, their spelling & punctuation is occasionally quite bad).

Gary Moulton's consolidated version of the journals and his own historic edits to the atlas, records, and every single day of the expedition from May 1804 - September 1806 is, without question, the single most comprehensive and accurate historic accounting of the Lewis & Clark expedition. I used Moulton's consolidation of their diaries and prints of their atlases / maps while following the route of their expedition.