(Reuters) - U.S. bank PNC Financial said on Monday it would buy smaller rival FirstBank Holding in a $4.1 billion cash-and-stock deal, expanding in the fast-growing markets of Colorado and Arizona.

The deal, which includes the banking subsidiary FirstBank, will also bring PNC closer to $600 billion in assets, narrowing the gap with rivals such as U.S. Bancorp.

Talk of potential mergers and acquisitions among Wall Street banks and large regional lenders increased at the start of the second half of the year in a major shift under the Trump administration after regulators under the Biden administration opposed or blocked big deals.

PNC CEO Bill Demchak said in June that he expected consolidation in retail banking to boost industry profits.

In July, regional lenders Pinnacle Financial Partners and Synovus Financial agreed to combine in an $8.6 billion deal, the biggest U.S. bank acquisition this year.

"Its (FirstBank) deep retail deposit base, unrivaled branch network in Colorado, (and) growing presence in Arizona make it an ideal partner for PNC," Demchak said in a statement on Monday.

Under the deal, FirstBank stockholders will get roughly 13.9 million PNC shares and $1.2 billion in cash.

FirstBank, which began offering banking services in 1963, manages $26.8 billion in assets and operates 95 branches.

FirstBank CEO Kevin Classen will become PNC's Colorado Regional President and Mountain Territory Executive, which includes Arizona and Utah.

The deal is expected to close in early 2026.

Wells Fargo advised PNC on the deal, while Morgan Stanley and Goldman Sachs advised FirstBank.

(Reporting by Arasu Kannagi Basil in Bengaluru; Editing by Sahal Muhammed and Sriraj kalluvila)