The Houghton Mine is an abandoned gold mine w/ plenty of fascinating & forgotten history.

This view is inside the 1000 level at a splitoff of recently-worked tunnels.  The red spraypaint indicating the 1050 sublevel leads to a flooded tunnel straight down w/ noticeable ladders leading into the water.  It may lead to another level below, or it serve as a sump to collect unwanted water or chemicals.  The tunnel directly opposite leads to a filled stope while the arrow pointing the 975 sublevel leads to other recently developed stopes & ore veins.  The route marking the main portal exit are clearly indicated along the walls.

After four solo trips spent exploring & photographing this complex mine that contain roughly two miles of underground workings on six different levels, I have concluded the following:

500 Level: Inaccessible

600 Level: Inaccessible

700 Level: Mostly Inaccessible

800 Level: Accessible

900 Level: Mostly Accessible

1000 Level: Mostly Accessible

A few mining terms:

Adit - A horizontal passage leading into the mine, not to be confused w/ a "tunnel", which would have an opening out the other side.  Adits are sloped slightly upwards to allow for drainage of groundwater.

Crosscut - A horizontal opening that does not run along the vein. Typically a shaft will lead to crosscuts at each level that give access to drifts along the vein. Crosscuts typically run straight as an arrow through worthless rock.

Drift - A horizontal opening that runs along the vein. Typically there are many ore chutes from stopes above, and the drift will wander to follow the vein.

Level - If you follow a ladder down a shaft, you will arrive at horizontal workings every 100 feet or so, and these are called levels. The levels have a station near the shaft, and are named by the distance down the shaft.

Manway - Any kind of passage with a ladder in it could be called a manway. Shafts are divided into "compartments" and one of these is very often a manway. Sometimes the manway of a shaft is crowded with pipes and cables and such.

Ore chute - A "spout" built of wood used to load broken rock from above into waiting ore bins.

Raise - A raise is like a shaft that starts undergound and goes upwards. Typically a ladder next to an ore chute along a drift goes up a raise and gives access to a stope above.

Square set stoping (timbering) - The most expensive mode of underground mining. As ore is removed in a stope, it is replaced by a 10x10 foot lattice of 12x12 timbers. The ground was unstable here & the lattice helps protect from potential collapses. Many times the sets are backfilled with broken rock to help support the stope.

Stope - An excavation underground that actually removed whatever it was they were after. These are typically irregular in shape as they follow the ore whereever it goes. If the vein is wide and/or the rock is poor, the challenge in mining is to keep the rock supported while extracting the material in the stope.

Winze - A winze is like a vertical or inclined shaft that starts underground & connects one level down to another.

Source: Mining Terms: http://cholla.mmto.org/mines/terms.html