How Deep is Black Mesa?


Thanks to .RK we know about how large the Facility is (and the answer is, surprisingly, not that large) but his maps are 2-dimensional and for the longest time I’ve wondered just how deep underground the BMRF actually extends.

What seems like a logical point for the deepest section of Black Mesa would be either the bottom of the big shaft the slime river drains into in the last map of Blast Pit, or the lowest section of On A Rail’s rail system. It’s difficult to determine exactly which, since the pipe Freeman uses to enter Power Up is a long way up the big shaft, but to get from Power Up to On A Rail there is an elevator going down a significant ways.

Fortunately, it’s pretty easy to open up the maps in hammer and take out elements of the geometry corresponding to level transitions, then lay each one so that it overlaps the corresponding element from the next map while preserving the height relationship between them; thus building a ‘chain’ of height-accurate structures all the way from the surface warehouse down to the bottom of the shaft in Blast Pit (and then extend that to the bottom of the elevator shaft in OAR:

It turns out that the slime shaft is deeper than the OAR sections, but only by about 250 Hammer units. Furthermore, the distance from the top of the elevator shaft in WGH (which is at ground level) to the bottom of the slime pit is 8580 Hammer units, which is equivalent to 6435 inches, 536.3 feet, or 163.46 meters.

That’s not actually very much. The Cheyenne Mountain underground missile command center goes more than 600 meters deep, the TauTona mine in South Africa goes down nearly 4 km, and there’s even an open-pit mine in Utah that’s just a big roofless hole dug to 900 meters. In fact, the cliffside area in Surface Tension extends nearly 35,000 Hammer Units down to the desert floor (6144 from main level geometry, plus 1796 * 16 from the skybox), meaning that Freeman’s Mind was absolutely correct when it claimed that Black Mesa was in fact physically built into a mesa. This works out to about 2,100 feet, roughly twice as tall as the mesas in Monument Valley EDIT: SEE BELOW.

I considered whether the canals in Unforeseen Consequences might actually run deeper than the slime shaft, but it’s hard to say on account of the elevator ride of unknown length that occurs between them and Office Complex.

In Forget About Freeman the player goes down two relatively short elevator shafts to get to the Lambda Complex, and then spends most of the rest of the level climbing upwards, so I legitimately suspect that many parts of the Lambda facility are in fact located ABOVE the ground-level that is seen in c3a1b.


Isn’t the elevator between Office Complex and We’ve Got Hostiles stationary? All you do is drop through the top of the elevator and then immediately exit. It’s the one that takes you from the Unforeseen Consequences to Office Complex that we don’t see, but a security guard does tell us that the offices are “upstairs” so it was probably just to the next floor.

Anyway I’ve considered the lowest part is probably the base of the canyon in Surface Tension, but if that doesn’t count, then the lowest level in my opinion is most likely in the Lamba Complex. From memory: from Forget About Freeman you’ last moment of daylight is during the aerial battle over Black Mesa. From there you go down an elevator into the toxic waste zone, encounter the HECU one last time and before taking the large entry elevator down, then you take another elevator down. You are now in the reactor core area, and that is the lowest point of FAF/LC. But then you do go up a bunch, to the point where the Xen supply depot must be just below the surface rather than far below it like you’d expect.


This has always intrigued me, so it’s nice to see someone do the math. The BP slime shaft makes sense as the deepest area - I always assumed it was either that map in BP, the first map in OAR, or the LC reactor maps as the deepest. I was just looking at the FAF/LC maps in hammer and from the surface in c3a1b to the starting point in c3a2c, it’s a net movement down 4360 units/272.5 feet - so that turns out to be not even close to the deepest area.

The elevator ride between the lower canals and OC isn’t very long, so OC’s A map can’t be too far above the lower canals. I don’t think the lower canals are all that deep - the AM labs aren’t too far from the surface (only one elevator ride in the tram), and from there it’s a relatively shallow elevator shaft, and the funicular elevator which does go much deeper, but still the overall distance down is not that much.

The way the LC maps progress upward is a bit puzzling, since you would think they would keep their most secretive project hidden away deep underground. However, something else to keep in mind is that the surface elevation is highly variable around the BMRF, as we can see in the ST maps. So perhaps the teleportation chamber is still fairly deep under a nearby uplifted area. Of course, we don’t really see any hills, mountains, or buttes around before we leave the surface for the last time in FAF (at least I can’t remember anything like that).

I do like the idea of the facility being built into an actual mesa - gives its name a more literal meaning.


It occurs to me that I may have double-counted the main-map and skybox sections of the cliff map, adding them together when in fact much of the geometry overlaps. A more conservative estimate of the height of the cliff using only the section of pipe that runs down below would be 870 HU, for a total (870 * 16 + 6144) of almost exactly 20,000 HU, equivalent to 1,250 feet which is much more reasonable. Even that may be exaggerated, because the region of cliff overlapping the main map is ~500 HU tall in the skybox and ~6000 in the real map, which would indicate a multiplier of about 12 and not 16 between the skybox and main map.

On another note I also decided to add to the height map one of the supports from Silo D, thoroughly expecting that the roof/dome of the silo could end up above the ground level as defined in WGH. It doesn’t actually, but comes pretty close, ending up pretty much level with the B map of We’ve Got Hostiles.


Tbh, I’m not at all sold on the idea that 1 HU = 0.75 inches. I know that the VDC says so, but I have a hard time believing that Gordon’s eye level is at 121 centimeters or 48 inches. For me, 1 HU = 1 inch makes the most sense. That being said, scaling is extremely weird in all Source Engine games. Like, how gigantic ARE these doors?!

Also, it’s worth noting that there is a HUGE inconsistency with height in the We’ve Got Hostiles levels (I measured 39.2 meters once, though I don’t remember what unit conversion I used). You spend all level taking cargo elevators to the surface, only to drop down a couple of meters and arrive back at the start of the level. It’s a bit silly. I used to have images of this embedded in a comment I left on this thread a while back, but they seem to have been eaten in the forum update.


The standard male human NPC model is 72 Hammer Units tall (and, interestingly, the female NPCs are somewhat taller at 74.4). This works out to only 54 inches or 4.5 feet, which is indeed very short for an adult human. 1 HU = 1 inch does indeed give a more reasonable even 6 feet, and would make the slime shaft in BM 217 meters deep (which is still not very much).


According to the VDC wiki page you linked to earlier, human character models use a different scale than map geometry and prop models:

  1. Maps, architecture and prop models use a scale of 1 foot = 16 units.
  2. Skyboxes (which are 1/16th scale of ordinary maps) use 1 foot = 1 unit.
  3. Human Character models for Source Engine currently use 1 foot = 12 units.

What I take from that is that the standard male human NPC model is supposed to be 6 feet tall, but for some reason Valve must have made a conscious decision to make the player and human character models smaller in the game world.


Went ahead and put together Office Complex to try to see how the lower canals you go through in Unforeseen Consequences compare to the slime pit and OAR tunnels:

If we assume that the elevator you ride to Office Complex only goes up one floor, they aren’t particularly close. For the canals to compete with OAR or Blast Pit in depth, that elevator would have to actually go up roughly twice the depth of the traversed sections of Office Complex.