Rockhounding Colorado: Saguache / Houselog Creek Geodes!
A scenic 40 minute drive southwest of Sagauche reveals a treasure trove of agate and chalcedony for any collector! Bring your digging tools and 5 gallon buckets for this rewarding locality!
Summarized Geology : (A little boring but useful)
Thundereggs, like those found at this site, are the result of very felsic fluids entering air pockets in rhyolitic or basaltic lava flows while in a plastic state. The fluid enters these air pockets and as the surrounding lava cools into a solid, the interior fluids become agate and chalcedony! The Rio Grande thundereggs formed within the massive rhyolitic lava flows during the oligocene epoch. During this time south-central Colorado was a lake of lava, the result of various volcanic eruptions, primarily those of the San Juan caldera where Creede now rests. This is relevant to your rockhounding pursuits because these flows and subsequent thunderegg deposits stretch for hundreds of miles. Reports of Rio Grande thundereggs range from Twin Mountains near Del Norte to Saguache, hundreds of square miles. Thus do not search exclusively in one area, there are literally hundreds of square miles where these thundereggs are located. Below in the section titled "The Maps" we include the USGS geologic survey map to show the expansive nature of the deposits as well as to help inform your search.
While rockhounding we each found a 5 gallon bucket of incredible Rio Grande thundereggs! They display beautiful chalcedony and stunning agate within, ranging from clear to dark blue. The agate had a variety of formations, we found moss agate and waterline agate. The chalcedony came in interesting stalactitic formations and as the classic "bubbly" formations. There is no clear way to determine the inner contents of a whole geode so we advise avoiding cracking the geodes to avoid shattering the fragile interiors. The waterline agate we found displayed beautiful white and black patterns hosted in a light blue-grey agate and the moss agate came in primarily white in the same light blue-grey agate.
Rockhounding: Location, Tools
As previously highlighted, the rockhounding area for finding Rio Grande thundereggs is very expansive. On the map we highlight one large area we found prosperous but do your own exploring to find your own treasure chest of thundereggs! Accessing this area may seem a drawback, but the beauty of the long drive only adds to this site's wonderfulness. The roads are not treacherous and are generally well maintained.
On the map, we mark a second location, twin mountains. We DID NOT rockhound there. We have only heard its reputation. It is in the same geologic formation and is known for parallel thundereggs, as such we placed it on the map and encourage you to explore it as well as other areas you believe would be fruitful. They likely will reveal beautiful treasures!
When rockhounding this area it is critical to avoid simply searching the surface for rocks. The area we highlight is very well known and searching the surface will only reveal small fragments of the thundereggs. Digging is necessary to find large quantities of whole geodes. Luckily, the ground is soft and we were able to dig several feet in a few hours and found many geodes in this endeavor! We highly recommend searching the surface until you find a location with a high concentration of fractured thundereggs. After finding this location we recommend digging to find whole thundereggs. It is useful to bring shovels, chisels, and picks to maximize your time collecting.
For this location we provide a unique set of maps for your rockhounding endeavors. First, is the google map with the highlighted area where we searched and dug. This area is incredibly prosperous. We additionally include directions to the site. The drive from the site south towards Del Norte is beautiful and an additional perk of the site. On the google map is the twin mountain location previously mentioned. We DID NOT rockhound here but the site is famous for parallel thundereggs and is worth taking a look at.
Secondly, is the USGS maps zoomed in on the rockhounding site. We included this map for the helpful topography and geologic map overlay. We encourage using this map to find nearby sites. We found that the elevation of 9400' was optimal for finding thundereggs. To change the opactity of the geologic map overlay use the slider bar on the right of the page (second from the bottom). The Taf layer that the thundereggs is found in is reported as:
Using this second map, we recommend searching for thundereggs anywhere in the Taf area near 9400'.