Billings Location custom Geohashing. The rims are awesome; the Pryors, not so much. So, here is an official implementation for Goehashing: Billings, MT. It uses essentially the same algorithm as the reference XKCD implementation, but instead of generating a Lat/Long it simply scales the possible MD5 values to somewhere on the latitude of the rims.
This reference can be (and is, by me) used as the "alternative" meetup point for any day. Official XKCD meetup time is still 4 pm Saturdays. Also note that the point doesn't follow the longitudinal contours of the rims. Go with the location due north/south to find climbing areas!