What it means
Prop 420 is a number that functions as a law. When Scottsdale residents say it, they mean the 2018 charter amendment that put the McDowell Sonoran Preserve beyond the council’s reach: no altering the land’s natural state, no diverting the Preserve taxes, without a public vote. It passed with about 71 percent on November 6, 2018, and it has been the first word in every Preserve argument since. “That’s a 420 problem” means a proposal needs an election, not a staff report.
The amendment grew out of a specific fight, over a building the city wanted at the Gateway Trailhead, but it settled a general question: who owns the Preserve. The answer the voters gave was themselves. The Preserve and the voters guide tells the thirty-year story; this page is about the measure.
Where you’ll meet it
In council debates whenever a trail, a parking lot or a ranger station is proposed. In the charter itself, Article 8, which the city posts online. In campaign mail, where a candidate’s position on 420 is still a litmus test. And on the trailhead signs, which do not mention it but exist because of it.
Where the word came from
Arizona numbers its ballot measures, and city propositions in Scottsdale have run through the 400s for decades; the Preserve tax of 1995 was Prop 400, the 2024 parks tax Prop 490. “420” is just the next number the county assigned for the November 2018 ballot. The coincidence with the cannabis slang was noted by everyone and used by nobody; the campaign called it the Preserve amendment.
The measure came from the Desert Discovery Center. For years the city planned an interpretive attraction at the Gateway Trailhead, the Preserve’s front door off Thompson Peak Parkway: exhibits, a cafe, event space, parking, admission. Supporters, including much of the civic establishment, argued that a Preserve people hiked but did not understand needed a place to teach them. Opponents saw buildings on land bought with the voters’ money to stay empty, and a precedent. A scaled-down version, renamed Desert EDGE, was unveiled in 2017, and by the end of that year the council had paused it while opponents gathered signatures.
They chose the strongest tool Scottsdale offers. A citizen initiative can propose a charter amendment, and the council cannot amend the charter back. The petition added sections to Article 8: Preserve land may not be altered from its natural state, and Preserve sales tax revenue, from Prop 400 of 1995 and Question 1 of 2004, may not be spent on anything but acquisition and trails, in each case unless a majority of voters approve at a general or special election. The exceptions were deliberately narrow, trail maintenance and expanding parking at existing trailheads. Opponents of the amendment said it was overbroad and would complicate running the Preserve. Voters passed it with about 71 percent, and the Discovery Center was finished.
What it is not
Prop 420 did not create the Preserve, buy the land or levy a tax; those were the 1994 resolution and the 1995 and 2004 votes. It did not ban selling Preserve land, because the charter already required a vote for that after 1998. It is not a state law, and it protects nothing outside the Preserve boundary.
The fine print
The text matters because it is read literally. Article 8, Sections 8 through 13 of the charter now do three things: define the Preserve by reference to the land the city has designated; prohibit altering its natural state except for trail maintenance and the expansion of existing trailhead parking, absent voter approval; and restrict the dedicated tax revenue to acquisition and trails, again absent a vote. The charter guide explains how a charter sits above ordinances; the practical effect is that staff now ask “is this 420-compliant” before drawing anything on Preserve land.
Two consequences were not obvious in 2018. First, the amendment froze the Preserve’s tax money into a purpose, land, that was nearly complete, which is part of why the council went back to voters in 2024 with Prop 490, a new tax for maintenance and parks rather than a reinterpretation of the old one; the ballot measures guide covers that vote. Second, it established the initiative as Scottsdale’s political weapon of choice, which is the backdrop to the 2024 referendum drive against Axon and the state’s 2025 response.
The record this site has not confirmed: the exact vote counts and the name of the political committee that circulated the petition. The city’s historical results page lists the measure, and the roughly 71 percent figure is consistent across the city’s own guides, but the certified tallies are in a results document this site has not opened, so they are not quoted here. What is certain is the principle the vote wrote down: in Scottsdale the Preserve belongs to the electorate, and the council works for it.