Vancouver, British Columbia--(Newsfile Corp. - May 21, 2026) - Riverside Resources Inc. (TSXV: RRI) (OTCQB: RVSDF) (FSE: 5YY0) ("Riverside" or the "Company"), with partner Questcorp, the Company has completed an expanded aeromagnetic drone survey at the La Union Project in Sonora, Mexico. The new data refines the drill targets and improves understanding of district-scale geologic structures. Together with property-wide structural mapping and the high-grade Phase 2 sampling results announced May 5, 2026, this information is being used to finalize drill targets ahead of the fully permitted summer 2026 drill program.

Drill roads and pads are being prepared this week, and arrangements with the drilling contractor are progressing rapidly. The geophysics provides greater conviction in the scale of the potential feeder structures and the robust magnetic sources at depth, supporting both the Carbonate-hosted Replacement Deposit targets and the Sediment-hosted, Carlin-like stratigraphic targets discussed below.

Highlights

• Expanded drone aeromagnetic survey adds 145 flight lines (193 km) plus 55 km divided into 20 tie lines, for 248 km of total drone coverage building on the 2025 baseline dataset all done with 100m line spacing for quality definition.
• Improved imaging of structures beneath post-mineral cover, including the new northwest-trending structures identified by spring 2026 field mapping as a potential ore control creates new drill targets.
• Integrates structural mapping with detailed 1:1,000 geologic field mapping of target areas and district-scale 1:5,000 geologic mapping to characterize interpretations at depth that may be associated with mineralization.
• An Induced Polarization (IP) geophysical survey is planned to commence shortly as a further input into Phase 2 drill targeting with planned 5 IP lines that will be done concurrent with drilling the first targets and sets up for continued drilling in Phase 2.
• Drill roads and pads beginning to be built for upcoming Phase 2 drill program.

"The expanded aeromagnetic survey provides a much clearer view of the La Union Project's structural framework at depth. Combined with the high-grade sampling results released earlier this month, we now have the data in hand to refine our Phase 2 drill targets with greater conviction," said John-Mark Staude, President and CEO of Riverside Resources Inc. "The program is progressing well, and our teams are preparing for the launch of drilling in the near term. We are also expanding the drill targets in areas where high-grade gold and base metals were previously mined, and where geophysics can now image potential source targets at depth."

Survey Overview

The survey was flown with a magnetometer suspended beneath a drone along parallel flight lines, with tie lines flown perpendicular to level the dataset. The expanded grid extends magnetic coverage across the property in all directions relative to the 2025 baseline survey, providing district-wide imaging of structural features and magnetic bodies at depth. The 2025 dataset was a key input into planning the Phase 1 drillholes; the expanded 2026 dataset will allow these structures to be traced more confidently beneath post-mineral cover and build a more complete exploration model for Union.

Photo: Drone operator with an airborne magnetometer at Union, Sonora preparing for drone take off.

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Figure 1: Map showing 100m spaced flight lines (black) and 500m tie lines (blue) relative to the colored data 2025 AeroMag survey that now has been expanded.

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Path Forward to Drilling

The aeromagnetic data is being integrated with the property-wide structural reinterpretation, surface and underground sampling, and the planned IP survey to finalize drill targets. With permits in hand, site access secured, and a drill contractor and geophysical service provider contracted, Riverside and Questcorp remain on track for drill mobilization at the La Union Project in the coming weeks.

Qualified Person

The technical content of this news release has been reviewed and approved by Freeman Smith, P.Geo. (British Columbia), a qualified person under National Instrument 43-101 who is non-independent and the Vice President Exploration for the Company.

About the Union Project

The Union Project is located in northwestern Sonora and shows district-scale carbonate replacement deposit (CRD) mineralization. The project hosts historical mining areas and multiple exploration targets associated with gold, silver, zinc and lead mineralization within carbonates and structurally controlled settings. Riverside operates the project through its Mexican subsidiary while advancing exploration in partnership with Questcorp.

About Riverside Resources Inc.:
Riverside is a well-funded exploration company driven by value generation and discovery. The Company has a strong balance sheet with over C$5,000,000 cash, no debt and tight share structure with a strong portfolio of gold-silver, copper, and REE assets and royalties in North America. Further information about Riverside is available on the Company's website at www.rivres.com.

Certain statements in this press release may be considered forward-looking information. These statements can be identified by the use of forward-looking terminology (e.g., "expect"," estimates", "intends", "anticipates", "believes", "plans"). Such information involves known and unknown risks -- including the availability of funds, the results of financing and exploration activities, the interpretation of exploration results and other geological data, or unanticipated costs and expenses and other risks identified by Riverside in its public securities filings that may cause actual events to differ materially from current expectations. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this press release.

Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.

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