The Honeydew Creek Wildlife Preserve protects 2,980 acres (12 km2) of habitat north of King Peak for bald eagle, northern spotted owl, mink and anadromous fish.

With the advent of mechanized equipment, the area became more accessible, and the Douglas fir forests supplied lumber and an economic boom was underway by the 1940s with Humboldt County being the largest supplier in the state.

On December 10, 1929, President Herbert Hoover issued Executive Order 5237 at the request of the state that withdrew several parcels from settlement as public land.

[9] Congressman Clem Miller introduced a bill in 1961 to establish the national conservation area, and had support from organizations such as the Sierra Club and the Mattole Action Committee.

[9] The area gets some of the highest rainfall totals in the continental United States,[5] with over 100 inches (2,500 mm) of rain yearly in the Mattole River valley.

The extreme vertical rise of the mountains create intense rain showers (called orographic, meaning terrain-induced), caused by the lifting of storms as they approach the steep topography.

It has historically had large runs of salmon and steelhead trout, but due to past logging, road building and severe floods in 1955 and 1964, all of which impacted the river, fish numbers have declined.

[11] The coho salmon is a federally listed threatened species (Southern Oregon/Northern California populations)[12] that use the Mattole River and its tributary, Mill Creek.

[15] The watershed, or catchbasin of the river has been seriously impacted from past road building, and restoration efforts include abandonment of some roadways as well as reshaping and upgrading of others.

)[18] Other vegetation in the area include knobcone pine, laurel, manzanita, poison oak, blackberry, Oregon grape and salal.

The BLM's Final Environmental Impact Report recommends beargrass habitat improvements, such as controlled burning and brush removal, to increase growth which would reduce harvesting pressure on existing limited distribution of the plant.

The proclamation also functions to elevate California's offshore lands to a national level of concern and focuses management on protection of geologic features and lifeforms.

The Rocks and Islands Wilderness is within the National Monument, just offshore of the King Range, and protects important habitat for seabirds and marine mammals as well as the coastal scenic beauty.

A permit system is in place affecting hikers and backpackers who plan to spend at least one night in the King Range Conservation Area, including the Lost Coast Trail.