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Phantom Falls pours over a Lovejoy Basalt ledge.

A few things have happened over the last couple of months that have refocused my attention on Northern California’s Lovejoy Basalt formation. First, my family and I took our somewhat-annual trip down to North Table Mountain to enjoy the epic wildflowers that erupt there every spring. Second, I wrote my recent article on the Orland Buttes, a key site containing this geologic marvel. In addition, I have gone through Chico numerous times this spring, which inevitably brings to mind Bidwell Park, which was the place I first encountered this unusual rock.

Classic examples of Lovejoy Basalt along Big Chico Creek and the Orland Buttes.

This naturally raises the question, just what is Lovejoy Basalt? First, basalt is a dense igneous rock that is produced through volcanic activity. Northern California, which contains the southern end of the Cascade Range, is home to numerous basalt formations. However, Lovejoy Basalt is distinct among these for a few reasons. First and most obvious, its appearance is quite unmistakable. It manifests as a blocky conglomeration of rock, welded together and very dense. The rock itself is aphyric, showing no granular composition. Less obvious but still distinct is the way the rock tends to break apart in along rather stark fault lines. This is not as obvious when hiking among it but looking from above, or in some rather dramatic places where the faulting is pronounced, it is a tell-tale clue that the rock is Lovejoy Basalt.

The Lovejoy Basalt zone.

Lovejoy Basalt is believed to have originated out of large volcanic vents near Thompson Peak in the Diamond Mountains, a range marking the far northeast corner of the Sierra Nevada. The Diamond Mountains are something of a transitional range, being primarily volcanic in nature but still in the sphere of the Sierra. The basalt was laid down in a vast sheet as a lava flow at some point in the past. It was subsequently broken up and washed away, both down creeks and rivers in the Sierra and ultimately out to San Francisco Bay. At its greatest known extent covered a vast area that is roughly triangular in shape. Apices of the triangle are located at Thompson Peak, the Orland Buttes and Putnam Peak in the Vaca Mountains. This last is particularly noteworthy, since it is located 150 miles away from the source of the Lovejoy Basalt lave flow.

The Putnam Peak area. Click on the image to enlarge it.

Unfortunately, the Putnam Peak is difficult to study. The area is on private land and access is very limited (consequently, google earth images will have to suffice). In addition, 2020’s Hennessy Fire burned the entire area. Nonetheless, the area offers a surprisingly large but extremely isolated Lovejoy Basalt formation.

The basalt in this area manifests in two distinct manners, both of which are exhibited at other Lovejoy Basalt sites. First, on Putnam Peak itself, there are large rocky outcroppings and massive boulders. These run eastward along a vein before meeting a massif composed of the rock. Here the Lovejoy Basalt exhibits the mounding, faulting and fracturing that is also evident at other locations. This location, 75 miles away from the nearest similar Lovejoy basalt formation, sets the furthest limit of the rocky type.

The northern apex on the Lovejoy Basalt Triangle is the Orland Buttes. Running against the North Coast Range that hems in the western side of the Sacramento Valley, these are also an isolated formation, though not quite so remote as Putnam Peak. These are located roughly 100 miles from the source near Thompson Peak and 30 miles away from the nearest similar formation in Chico’s Bidwell Park, the Orland Buttes are a surprising outpost of basalt, especially when considering there is nearly no other evidence of volcanic activity in the vicinity.

Lovejoy Basalt formations radiate out from the Thompson Peak area.

While the outer points of the Lovejoy Basalt zone are isolated, the highest concentration of the formation is located at the western edge of the Northern Sierra Nevada. With occurrences found along Big Chico Creek, North Table Mountain and the Campbell Hills, the area between Chico and Oroville yields the most extensive and dramatic examples of this unusual rock formation. Even better, most of the formations are on public land and access to these landmarks is easy.

A chasm along Big Chico Creek composed of Lovejoy Basalt.

The northernmost occurrence in this high concentration is in Chico’s superlative Bidwell Park. Through this 3,670 acre park flows Big Chico Creek, a significant waterway in the northern Sierra Nevada foothills. Most of the immediately visible rock in the park is part of the Tuscan Formation, a layer of volcanic rock initially formed by a series of mudflows that resulted from large eruptions. However, underlying much of the park is a layer of Lovejoy Basalt. This is most readily visible in the narrow gorge that Big Chico Creek has carved through the basalt.

Looking down on the narrow gorge carved into the Lovejoy Basalt.

Within the gorge, the blocky basalt is exposed in the form of walls, spires and boulders. The rock in this location appears somewhat different from the other areas where Lovejoy Basalt is evident since most of rock along the creek has been scoured smooth by the water. Furthermore, a significant number of Lovejoy Basalt boulders have fallen into the creek, giving Big Chico Creek a unique and beautiful appearance. Indeed, while Bidwell Park has many excellent features, it is often this unusual, rocky channel that is the signal memory of those who have spent time there, hiked along the creek or cooled off on one of the swimming holes during the hot summer.

A few miles to the south is magnificent North Table Mountain, perhaps the single greatest example of Lovejoy Basalt. In terms of natural beauty, this area is worthy of great acclaim, though it is not well known outside of the local area. In spring, it is paradise on earth, with riotous wildflower displays and a surprisingly high concentration of awesome waterfalls. It is also the site of the most extensive Lovejoy Basalt formation, stretching over a broad expanse for several miles, it reveals many details about this kind of rock that is obscured at other sites.

Lovejoy Basalt and amazing wildflowers at North Table Mountain.

North Table Mountain is a large, remnant chunk of the original Lovejoy Basalt flow, now isolated as most of the flow has been washed away. What is left is a broad, flat-topped mesa surrounded by cliffs of exposed basalt on the north, west and south sides. The top of the flow is gently undulating, with a sporadic protrusions of the tell-tale dark basalt. These protrusions feature the classic, dark, blocky composition that is the calling card of Lovejoy Basalt. The area between the protrusions has filled in with loose soil, providing the necessary for the flourishing of wildflowers.

In a few places, springs on the eastern edge of the plateau have cut channels extending westward across the flat-topped mountain. They deepen as they progress and eventually spill over high cliffs. It is here, at these cliffs, that some of the most fascinating aspects of Lovejoy Basalt is revealed. The blocky composition that is a classic component of the rock’s appearance is, in fact, the result of a columnar cooling process similar to what is seen in columnar basalt formations at places like Devil’s Postpile. The Lovejoy Basalt is darker and the columnar formations tend to be smaller in diameter but the comparison is obvious. Moreover, the height of some of these columnar formations is really impressive, reaching over 100 feet.

Phantom Falls blows in the wind, alongside a large, exposed portion of columnar Lovejoy Basalt.

In some places at North Table Mountain, the Lovejoy Basalt layer has been undercut by the creeks, leaving the flow overhanging the the more erosion-prone layers underneath. The areas with large columnar formations tend to peel away and collapse, leaving a large pile of broken columnar chunks below. It once again exhibits classic basalt behavior.

North Table Mountain is also an excellent place to observe the faulting and cracking that can happen with Lovejoy Basalt. In the areas where the broad expanse has been unbroken by erosion or other forces, the rock still has a tendency to break along linear joints. This creates a collection of long, linear gullies that run parallel to each other. This is particularly evident in the flat areas in the southern half of North Table Mountain.

Water flows through a gap in the Lovejoy Basalt formed by a joint in the rock.

A little further south from North Table Mountain is the Campbell Hills. This area is rather obscure but is still a fantastic example of Lovejoy Basalt. Though it lacks the dramatic cliffs and waterfalls of its northern neighbor, it still exhibits a fantastic collection of joints and fissures. Indeed, there is more rock exposed here than in the joint/fault areas of North Table Mountain.

The land is located on state land adjacent to the Thermolito Forebay. In theory, there should be public access, but there are no amenities like parking areas or trails. It is Lovejoy Basalt in its primeval state, waiting to be explored and appreciated!

There are more sites consisting of Lovejoy Basalt higher up in the Sierra Nevada, but none are as extensive or impressive as those found in the Central Valley or along its perimeter. Most of these higher formations are exposed through the work of creeks that flow by them. Located on Forest Service land, they can be accessed freely but they are remote.

For those inspired or interested in this unusual, distinctly Northern California landscape, spring is the ideal season to explore Lovejoy Basalt. All the sites that are open to the public are at their best this time of year. The grass is green and lush, wildflowers are brilliant (or beyond brilliant!) and the creeks and waterfalls are full and impressive. When the high country is still snowed in, these rugged formations and all their attendant beauty make great hiking adventures and are sure to embed great memories, just as this strange and beautiful landscape was embedded in California long ago.

A Lovejoy Basalt Gallery (click to enlarge):