In Ventura County, California, a quiet quarry in Fillmore quietly fueled the growth of Southern California’s infrastructure for decades. Grimes Rock Inc., one of the largest construction aggregate processing plants in the region, produced essential materials such as washed concrete sand, plaster sand, pea gravel, road base, and topsoil. All products met strict Green Book and Caltrans specifications, ensuring the quality required for public works and private construction projects alike. Contractors, engineers, and developers relied on the Fillmore site as a steady and consistent supplier of construction-grade aggregates, cementing the company’s reputation in a competitive market.
In January 2025, Grimes Rock Inc.’s operations entered a new chapter when CalPortland, a major West Coast producer of cement, concrete, and aggregate products, acquired its aggregate and ready-mixed concrete assets, along with affiliate companies State Ready Mix Inc. and State Ready Mix Recycling in Oxnard, for approximately $160 million. This acquisition expanded CalPortland’s presence in Southern California, integrating the Fillmore site along Grimes Canyon Road into a broader network of operations. The deal ensures continued supply of high-quality materials to Ventura, Santa Barbara, and Los Angeles counties while aligning the facilities with sustainable building practices.
The transition marked both the end of Grimes Rock Inc. as an independent operator and the continuation of its role as a vital supplier under the CalPortland umbrella. Beyond the financial terms, the acquisition reflects the strategic importance of proximity to urban centers and regional demand for construction materials. With infrastructure growth, housing development, and commercial projects ongoing in Southern California, this quarry remains central to supporting the area’s building needs.
Origins and Operations of Grimes Rock Inc.
Grimes Rock Inc. operated its primary sand and gravel quarry in Fillmore, California, supplying a wide range of construction aggregates. The plant produced washed concrete sand for durable concrete, plaster sand for finishing applications, pea gravel for decorative and functional landscaping, road base materials for infrastructure, and topsoil for landscaping and site preparation. Every product adhered to Green Book and Caltrans specifications, which set stringent quality standards to ensure consistency, durability, and suitability for construction projects.
The facility at 3500 Grimes Canyon Road was more than a processing plant—it was a hub of local economic activity. Conveyor belts, crushers, and screens transformed raw rock into finished products, while logistics operations coordinated the delivery of materials to contractors and distributors throughout Ventura, Santa Barbara, and Los Angeles counties. The company’s attention to quality and timely delivery built trust with construction companies, public agencies, and residential developers alike.
Strategic Acquisition by CalPortland
CalPortland’s acquisition of Grimes Rock Inc. and its affiliates represents a significant expansion of the company’s Southern California footprint. By integrating the Fillmore quarry, State Ready Mix Inc., and State Ready Mix Recycling into its operations, CalPortland enhanced its vertical capabilities, covering extraction, concrete production, and recycling of construction materials.
The $160 million deal, finalized in January 2025, reflects the strategic value of owning high-quality aggregate sources near growing urban markets. Aggregates are heavy and costly to transport; proximity to construction sites reduces costs, improves delivery speed, and ensures material availability. CalPortland now operates the Fillmore site under its brand while continuing to offer pickups and deliveries Monday through Friday from 6 a.m. to 4 or 5 p.m., maintaining service continuity for regional contractors.
The Role of Affiliate Operations
State Ready Mix Inc. and State Ready Mix Recycling brought additional capabilities to the acquisition. State Ready Mix specialized in ready-mixed concrete, offering tailored mixes for a variety of construction applications. Its fleet of concrete trucks enabled timely deliveries for large-scale infrastructure projects as well as residential and commercial developments.
State Ready Mix Recycling provided essential sustainability services, processing demolished concrete and asphalt into reusable road base materials. This operation reduces landfill usage, lowers carbon footprints, and promotes environmentally responsible construction practices. Integrating recycling and ready-mix capabilities alongside the aggregate quarry enables CalPortland to offer a more comprehensive, sustainable, and efficient supply chain for Southern California construction projects.
Local Impact
The acquisition’s effect on local communities balances continuity with change. Employees at the Fillmore and Oxnard facilities retained their positions, while contractors and construction companies continue to receive dependable supply. At the same time, integration into a larger corporate structure may bring new technologies, operational improvements, and potential investment in infrastructure, increasing efficiency and sustainability.
Local officials and residents have historically been attentive to quarry operations, monitoring impacts such as truck traffic, noise, dust, and land use. CalPortland’s management of these factors will shape community relations and environmental compliance in the years ahead. Maintaining a balance between industrial activity and environmental responsibility remains central to the company’s strategy in Ventura County.
Future Prospects for Southern California Construction Materials
Grimes Rock Inc.’s acquisition reflects broader trends in the construction materials industry, where consolidation enables larger companies to manage supply chains more efficiently and respond to growing demand. As Southern California continues to experience infrastructure growth, housing shortages, and commercial development, high-quality aggregate supply remains essential.
CalPortland’s integrated operations, including quarry extraction, ready-mix concrete production, and recycling, position the company to meet regional demand while incorporating sustainable practices. The Fillmore site remains a critical node in this network, providing reliable materials for projects ranging from highways and bridges to residential and commercial construction.
Conclusion
The story of Grimes Rock Inc. is one of enduring significance in Southern California’s construction sector. From its beginnings as a local quarry to its integration into CalPortland’s regional network, the company has provided essential materials that supported decades of growth. The acquisition signals both the strategic value of local aggregate sources and the evolving nature of the construction materials industry, where sustainability, logistics efficiency, and regulatory compliance play increasingly important roles. For contractors, engineers, and policymakers, the Fillmore site stands as a reminder of the crucial foundations underlying the region’s built environment.
Frequently Asked Questions
What products did Grimes Rock Inc. produce?
Grimes Rock Inc. produced washed concrete sand, plaster sand, pea gravel, road base, and topsoil, all meeting Green Book and Caltrans standards.
Who acquired Grimes Rock Inc.?
CalPortland Company acquired Grimes Rock Inc. and its affiliates in January 2025.
Which affiliates were included in the acquisition?
State Ready Mix Inc. and State Ready Mix Recycling in Oxnard were part of the acquisition.
Where is the Grimes Rock plant located?
The plant is located at 3500 Grimes Canyon Rd., Fillmore, California.
How does the acquisition affect regional construction material supply?
The acquisition strengthens CalPortland’s presence in Southern California, improving logistics, supply continuity, and access to sustainable materials.
