(CNN) -

Here is a look back at the events of 2014, so far.

Notable U.S. Events: January 1 - Colorado legalizes the purchase of marijuana for recreational purposes.

January 1 - The 2010 Patient Protection and Affordable Care Act goes into effect.

January 6 - The Senate votes to confirm Janet Yellen as the first woman to head the Federal Reserve.

January 9 - Chemicals begin leaking from a tank owned by Freedom Industries into the Elk River in West Virginia. Approximately 300,000 people in nine counties are told not to use their tap water.

January 16 - Ohio executes inmate Dennis McGuire with a new combination of drugs, due to the unavailability of drugs such as pentobarbital. The state used a combination of the drug midazolam, a sedative, and the painkiller hydromorphone, according to the state corrections department. According to witness Alan Johnson of the Columbus Dispatch, the whole execution process took 24 minutes, and McGuire appeared to be gasping for air for 10 to 13 minutes.

January 17 - President Barack Obama announces changes to the National Security Agency and its surveillance programs.

January 30 - CNN reports that at least 19 veterans have died due to delays in simple medical screenings like colonoscopies or endoscopies, at various VA hospitals or clinics. This is according to an internal document from the U.S. Department of Veterans Affairs that deals with patients diagnosed with cancer in 2010 and 2011, obtained exclusively by CNN.

February 14 - General Motors recalls 780,000 vehicles due to faulty ignition switches.

March 22 - A mudslide near Oso, Washington, kills 43 people.

April 2 - Army Specialist Ivan Lopez kills three people at Fort Hood in Texas before taking his own life.

April 22 - The Supreme Court upholds a Michigan law banning the use of racial criteria in college admissions.

April 29 - Oklahoma inmate Clayton Lockett dies of an apparent heart attack during a botched execution by lethal injection.

April 29 - The NBA bans Los Angeles Clippers owner Donald Sterling for life in response to a leaked recording in which Sterling made racist remarks.

May 19 - Same-sex marriage becomes legal in Oregon.

May 20 - Same-sex marriage becomes legal in Pennsylvania.

May 23 - Elliot Rodger goes on a killing spree near the campus of U.C. Santa Barbara, killing four men and two women before taking his own life.

May 27 - President Barack Obama announces that 9,800 troops will remain in Afghanistan after the withdrawal of most troops at the end of 2014.

May 30 - Veterans Affairs Secretary Eric Shinseki resigns.

May 31 - President Barack Obama announces the release of prisoner of war Bowe Bergdahl, held for five years by a militant group linked to the Taliban. In exchange for Bergdahl's release, five detainees at Guantanamo Bay are released to Qatar.

June 1 - Same-sex marriage becomes legal in Illinois.

June 2 - The city council in Seattle, Washington, votes to raise the city's minimum wage to $15 per hour.

June 30 - GM announces compensation of at least $1 million to families of at least 13 people who died as a result of a faulty ignition switch. GM is also offering money to those injured.

June 30 - President Obama says he is starting "a new effort to fix as much of our immigration system as I can on my own, without Congress," in response to a surge of unaccompanied children crossing the border.

June 30 - The Supreme Court rules that some companies can refuse insurance coverage for contraceptives due to religious objections.