Gov. Jerry Brown on Saturday signed a bill by Sen. Joe Simitian requiring extra warnings for the 40 percent of women over the age of 40 who have breast tissue dense enough to mask cancers on mammograms.

Last year, Brown had vetoed a similar bill, expressing doubts about whether the warnings were what he termed "a path to greater knowledge or unnecessary anxiety." Since then Simitian amended the bill to make it acceptable to the governor.

"I'm tremendously thankful for the governor's support of this measure and for his willingness to listen to and work with us on this issue over the past year," Simitian, D-Palo Alto, said in a statement.

Under the legislation, physicians will be required to notify women with dense breast tissue and inform them that further screening, through an ultrasound or MRI, might be recommended. About 40 percent of women have the condition.

The bill, SB 1538, also requires that a range of screening options be made available.

The idea for the bill came from Amy Colton, a Santa Cruz resident, registered nurse and cancer survivor. She had proposed it in 2011 in Simitian's annual "There Oughta Be A Law" contest.

In routine mammograms, Colton was never informed that her breast density could hide cancers and only learned that after treatment for breast cancer.

"This is about a patient's right to know," Simitian said. "Patients with dense breast tissue need to know that it can hide a cancer, and that additional screening options are available. Early detection is the key."

Connecticut, which requires physicians to inform women they have a condition known as dense breast tissue, has doubled early detection of cancer since the law took effect in 2009.

Over two years, Colton traveled to Sacramento to testify in support of the bill. Simitian called Colton's efforts heroic.

"Month after month she came to the Capitol to tell her story -- taking time away from her work and her life to make this happen," Simitian said.

Brown on Saturday also signed a bill that allows registered nurses to dispense birth control, making it easier for women to get contraceptives.

The governor signed the legislation during a visit to a Los Angeles Planned Parenthood clinic, where women's health advocates cheered the signing of AB 2348.

"At a time when some seek to turn back the clock and restrict women's health choices, California is expanding access to birth control and reaffirming every woman's basic constitutional rights," Brown said.

The bill, authored by Assemblywoman Holly Mitchell, D-Los Angeles, allows nurse practitioners and nurse-midwives to dispense the pill, patches and rings.

"With his signature, the governor also took action to address provider shortages statewide by allowing RNs to work to the full extent of their scope and training," said Julie Rabinovitz, head of the California Family Health Council. "This is especially important in our changing health care landscape."

The Associated Press contributed to this report. Contact Sharon Noguchi at 408-271-3775. Follow her at Twitter.com/NoguchiOnK12.